Itinerary and transportation recommendations for Rhine Valley and Mosel Valley

How many nights do you actually have for the whole trip? Your plan covers a lot of ground. All the places you mention can be reached by train.

Just one point. With all that movement in the Rhine/Mosel area, I'd consider not using Bacharach (a very small town) as your base and use some place further downstream with better connections, like St Goar, as your base.

Our son has 15 days, not including the travel days to and from Europe. We are planning on spending 4 nights in Berlin but could cut down our stay in Dresden to one night, if necessary. My husband and I don't have a limit on the number of days for our trip.

Regarding Bacharach vs St. Goar, they are only about 15 km (9+miles) apart. Both seem to be relatively small towns, but Bacharach seemed more picturesque from the research I've done. I assume they have similar availability of train connections, is that correct? We are not locked into staying anywhere in particular at this point. Bacharach was just more appealing initially.

Would 4 or 5 nights be sufficient to see the Rhine and Mosel Valleys?

That sounds reasonable for the average visitor with modest sightseeing goals.

We also want to see a bit of the Mosel Valley and visit Burg Eltz. We aren't sure whether we should do those as day trips from Bacharach, or if we should move to Cochem for a night or two and visit from there.

Splitting your time between the Rhine and Mosel makes sense to me.

We will start in Berlin, go to Dresden for a couple of days and then take a train west. Should we pick up a rental car in Frankfurt or take a train from there to Bacharach which will be our base for a few days?

It would not be my choice to rent the car in places where a car isn't necessary and where train travel is offered free of charge. The Rhine/Mosel region and the Black Forest are well-served by train and offer guest tickets for free transport if you stay in the right places.

The are good train trips from Dresden to the Rhine towns every two hours at 8:10, 10:10, and 12:10. The ICE from Dresden is direct all the way to the Rhine (Mainz, a 5-hour journey.) Transfer in Mainz to a local train for the smaller Rhine towns.

There is a wide area you can explore by train for free - see this Guest ticket guide with rail map with Koblenz at the center - if you make your stay in Boppard, north of Bacharach on the same rail line. And that is what I recommend. Boppard is a great town, too. Lots of restaurants and hotel choices, with outdoor cafes and eateries on the market square and many on the waterfront (Bacharach has nothing with river views, sadly); handsome half-timbered buildings; an awesome chairlift ride that takes you to the clifftops for nice views; several interesting sights in town and proximity to St Goar (Rheinfels Castle,) Oberwesel, and Bacharach. You can also use the Boppard ferry crossing to get to Filsen station for travel on the opposite riverbank to Rüdesheim or to Braubach (home of Marksburg Castle, never-destroyed medieval castle.) Boppard has a KD boat dock as well (and you can take KD boat directly to Braubach from there if you prefer that to the ferry + train.)

Boppard info: https://www.boppard-tourismus.de/media/was-ist-wo-broschu__re_en_190218.pdf

The Guest ticket will get you over to Cochem on the Mosel when you leave Boppard. I would suggest dropping your bags at your Cochem hotel in the morning... then use your VRM Guest ticket right away to make the train + bus ride to Burg Eltz (
which takes about 50 minutes.) OR... you can take the old-school route to Eltz; train to Moselkern, then hike to Burg Eltz (a marvelous way to visit!)

In Cochem there are 11 different innkeepers who offer the VRM Guest card as well. If you aren't staying with one of them, there are still cheap day passes available for small groups like yours if you want to visit TRIER, or BERNKASTEL, or other places.w

In the Black Forest, there are more than a hundred different towns that offer the KONUS card, which also provides free-ranging travel on the railways there. See flyer and short video.

https://prospektbestellung.toubiz.de/media/prospekt/file/5736289_KONUS_GB_2022.pdf
https://www.youtube.com/watch?v=KkgzMXQ7blQ

If you want to use the car from the Black Forest to the German alps and Munich, there are places where you can pick up a car, for sure. Many on this forum have used Gengenbach as a Black Forest base town - which works well for train outings but is also close to Offenburg, where you should be able to pick up a rental car.

I recommend getting a car in Frankfurt and staying on the Mosel, somewhere other than Cochem. Although maybe in the fall it won't be so overrun with tourists. Beilstein is one I have seen recommended on the Forum. I would look for accommodation that suits your situation. I can recommend an AirBnB in Enkirch, a very cute village with very few tourists. It's close to Traben-Trarbach.

I have to second Russ' advice for staying in Boppard. It's is a delightful river town, right on the river, and you can sit outside, have drinks and dinner, watching the barges go by. We took Russ' advice, and were very happy that we did so. We stayed at the Hotel Bellevue. Boppard also has great transportation connections.
I have been in Bacharach a few times , and it's just becoming too sleepy, and again, there are no river views. I don't think it ever bounced back after Covid.
I will disagree with Russ on one point: I enjoyed Burg Eltz much more than Marksburg. Burg Eltz has been lived in by one family continuously over several hundred years. However , Marksburg does have great views, but the castle is on a very high hill, and if the local mini- cabs aren't around, it's one heck of a hike up.
You have all great choices. And Russ is an incredible resource.
Enjoy your trip !

...we plan to drive to the Black Forest area, the Bavarian Alps, Munich,
Rothenburg and take the Romantic Road back to Frankfurt. We won't want
a car in Munich, so I'm not sure if we should turn it in and get
another car when we leave Munich for Rothenburg.

Rothenburg > Frankfurt by RR: What's lies north of Rothenburg on the RR is actually a pretty small part of the RR.

There are some comments by Nigel, Lee and KGC on this recent thread about the RR which I encourage you to read. South of Rothenburg: I have to agree that the driving route tends to be less than scenic. Noerdlingen does make for a good stop; the towns of Augsburg and Donauwoerth are worthwhile too. I recently traveled Munich > Augsburg > Donauwoerth > Noerdlingen on the RE train which connects all these RR towns, and I think I preferred seeing the countryside from the window of a train instead of driving it (as I did about 20 years back.) But I suppose this is true for much of Germany... the train eliminates the asphalt, the trucks, the driving tasks.

Marksburg/Eltz: Actually, I don't discourage people from visiting Eltz unless they are pressed for time (Marksburg is quicker from the Rhine because it's ON the Rhine.) I think BOTH castles are worthwhile and should be visited. They are very different from each other and hard to compare.

Where to stay on the Mosel: Cochem is a common choice for many reasons, including location, charm, sights, and services. Of course, there are other options depending on your interests. But the recommendation that you avoid Cochem altogether is a little too over the top for me. It's true that there are several very nice Mosel towns to stay in between Koblenz and Trier other than Cochem. I've stayed in Bullay on separate occasions, in Bernkastel, in Kröv, and in Traben-Trarbach as well. Bullay is an especially quiet, completely untouristy town only 10 train minutes from Cochem on the Mosel Valley Railway, great for outdoor activities - and great for train-travelers too since it serves as a train hub with an offshoot railway (The Mosel Wine Railway) which serves Traben-Trarbach and a couple of other towns.

So if you want to avoid tourists altogether, G3rryCee's Enkirch and Bullay will probably come close to achieving that goal. You can reach Enkirch (and the larger town of Traben-Trarbach) using the Mosel Valley Railway to Bullay and changing trains there for the Mosel Wine Railway to Kövenig (see link to map above.) Use the ferry there that crosses the river to Enkirch. Kröv is also nice and quiet; there's a bus from Traben-Trarbach that gets you there in a few minutes.

That said... If you are using Cochem as a BASE TOWN for outings, most people will probably not find the tourist invasion there to be all that objectionable. If you leave town by 10 am for a day in TRIER or BERNKASTEL, or wherever, and return 6-8 hours later, the bulk of the tour-bus crowd will already have left Cochem. In the early mornings and evenings, when you will be there, Cochem won't be overcrowded unless there's a big festival in town. At mid-day on Saturday or Sunday, it's best to spend your time elsewhere if you are crowd-averse.

Beilstein is a place that gets a lot of attention. It's very cute - but very tiny as well, so tiny that just a couple of tour buses unloading there can overwhelm the place.

https://upload.wikimedia.org/wikipedia/commons/7/73/Beilstein_%28Mosel%29,_2012-08_CN-01.jpg

And it really doesn't have much at all going on there besides eateries and wineries that would require more than a couple of hours. It is definitely a place that caters exclusively to tourists. It is worth a visit; you can cruise to Beilstein in one hour from Cochem, a nice way to get there. But Beilstein has just 150 residents. I prefer bedding down and taking meals in a place like Cochem, with 5,000 plus residents, a real commuity with churches, clubs, etc., a variety of sights and diversions (chairlift, Reichsburg Castle tour, Bundesbank Bunker) and a more diverse business community.