Rhine river valley

Yes, but by train you don't have to plod along through the whole region, including the duller parts - you can be selective about the most scenic zones and the best destinations! I would make some serious adjustments to whatever the cruise boat itinerary offers, for sure.

I'd be sure to spend at least 2-3 days in the most scenic part of the Rhine, the part between Koblenz and Rüdesheim, which UNESCO has designated a World Heritage Site - the Upper Middle Rhine Valley, shown on this map.

Some details: http://www.loreley-info.com/eng/rhein-rhine/walking-hiking.php

And I would also take a detour up the MOSEL Valley railway as well at Koblenz for 2-3 days...

https://www.mosel-inside.de/en/travel-guide/mosel-villages.html

Mosel railway map with stops between Koblenz and Trier:
https://assets.static-bahn.de/.imaging/focalpoint/727x545/dam/jcr:35bd03e4-289e-4ea5-96f0-16780dd8213e/191035-258837.jpg

You can do day-cruise boats on both the Rhine and Mosel. Mosel: focus on cruises between Cochem and Bernkastel. Rhine: Focus on cruises between Rüdesheim or Bingen and Boppard.

Check out recent youtube videos by ‘very unofficial travel guides’. Morgan has done a couple of Rhine cruises on lesser known, cheaper lines. You might find something of value.

That said, spending a day plus in the most interesting part of the Rhine is unsatisfactory to me. Better to concentrate on the Middle Rhine between Mainz/Wiesbaden and Koblenz or Cologne as well as the Mosel. So much to see. I just spent a week there, my fifth trip since 2011

Much of the Rhine River is not very scenic at all - flat and industrial. The river cruises, like Viking, travel through most of it at night so you have days in the towns at which it stops. The exceptional part, the gorge, is the part you see in the TV commercials with the mountains, vineyards and castles. So you could hit all the stops by train and just do the scenic part by a local cruise (K-D is the one I recall). In fact, if the water is low on the Rhine, the long cruises, like Viking, may have to stop and you continue through the gorge on the smaller local ships. Thats what happened to us.

I think you can do a better trip. You can spend as much time as you like in the nicer towns, explore both the best part of the Rhine and the Mosel, eat the local food, drink the local beer and wine. Doing the trip by train is easy and a good option. Heck, depending on the time of year, that "River Cruise" would likely have some parts by bus due to low water.

Start out with how much time you want to spend, and list out things you would like to see or do. Also list what interests you (history? Art? Food? Beer or Wine Culture?, etc.

You can get lots of help on here. If you have not traveled Europe before, Rick Steves "Europe Through the Back Door" is an excellent read and a how-to of travel.

My wife and I traveled from Basel to Amsterdam on Viking in December. My wife likes these river cruises better than I. I will give Viking credit for a nice small room (no repacking every move), good meals and good service. My wife likes the tours and learns from them. I did not regret the 10 days.

All that said, I prefer to travel by train and stay right in the town that I want to visit not at some pier in a warehouse district. Our stops were about 50/50 in convenient areas near the towns we were visiting. As others have said, I would make fewer stops by train in areas you want to see the most. Learn to use the Dbahn and Booking.com (or other hotel) websites. I like the Michelin Green Guide in selecting stops.

I've traveled the Rhine by river cruise and by train. I would choose by train every time. I was frustrated by the river cruise because it's very limited in what and where you can see on the excursions. The cruise did introduce me to Heidelberg which I had not been to as Rick doesn't give it much love. I really enjoyed it and am taking my husband back with me this December.