Let's talk Reims.

"Just overall living as temporary locals." Well, you've definitely been reading your Rick Steves.
Whether something is "worth it" is of course something you have to decide.
Here's some info to help you decide:

You have 10 days in Paris, you want to spend most of that time in Paris, living like a temporary local, right?

Thanks to the 200 mph train, Reims is easier to get to than ever, the station to station time is 45 minutes from Paris L'Est.
Of course actual travel time will be longer than that (getting to Paris L'Est station, waiting for the train, same thing on the way back, etc.).
You should book that train fare as soon as you can, they've been selling April tickets for some time now.
You also should book the champagne tastings in advance, to get a tour in English. Mumm is the easiest to get to champagne cave.

Your other day-trip choices from Paris (reasonable day trips) are:
Versailles (it's most of a day and so Rick classifies it as a day trip in his literature)
Giverny (Monet's house/garden)
Chartres (another Gothic cathedral classic, but no tour of champagne caves)
One of these 3 close-in to Paris (not Loire Valley) chateaus: Vaux le Vicomte, Chantilly, or Fontainebleau

Absolutely! The train is a short hop and Reims (tough pronunciation, Rhantz, check out acapela.com for practice) is worth the effort. We've not been but will do it this September and it's on our list after 11 years going to Paris. There is so much to experience in Paris that you will have to return, as often as you can, like we have, after writing it off after 3 visits.

You are right, Kent. Whether it is "worth" it or not is completely dependent on the traveler. You are also correct in that we've been watching and reading Rick! (We had our trip booked to Mexico and switched it a few weeks ago to Paris!)

I should have said - who has been to Reims and what was your experience? Recommendations?

My recommendations in Reims are as I already said in my 1st post: which are what you have already pretty much figured out:
1) the cathedral - getting into the ambience of the architecture and history of the cathedral
2) champagne tasting, Mumm's is the easiest to get to without wasting a lot of time getting to other caves farther out of town
3) walking around the town and experiencing some of the details (the Living Like a Temporary Local thing hasn't worked for me, but so what) and seeing things like the room where the Germans surrendered in 1945.
4) Rick's books Paris and France cover what you need to know for a day trip to Reims.

For the cathedral, I prefer Chartres because of its glass, but the town doesn't offer champagne. If you go to Reims, consider a visit to the abbey church of S Remi. It has a lovely Romanesque interior, and I found it to be far more inviting than Reims Cathedral.

Another attraction in Reims is the Roman gate, a few blocks north of the cathedral and east of the station. You can see the ruts the chariots made.

I liked Chartres better because of the asymmetrical towers, the sundial, the labyrinth at the crossing, the spectacular windows, and Malcolm Miller's tour. About an hour by train from Gare Montparnasse, no need to book ahead. But, alas, no champagne cellars (plenty of champagne and other things to drink though).

As said, all depends on the traveler. I'd be inclined to do it because it gives you a chance to experience something different than big-city Paris. We've been to Reims, and the last time in Paris took a day trip to Dijon for this same reason). Plus its fun to go on a fast train!

Reims has a nice pedestrian-only downtown street where you can sit outdoors and have an enjoyable lunch (depending on weather). The cathedral is impressive. Ironically the one thing that's not so easy to do is champagne tastings at the champagne houses since you'd need a car to get to most of them, and drinking/driving isn't a good idea anyway in France.

Re the above post, Mumm's is within walking distance of the train station, so you can drink and not drive. Another reason to take trains in Europe.
But the OP will have to reserve a Mumm's tasting ASAP to get a tour in English, since their trip is coming up soon. Although if they want to Live Like a Temporary Local, they could take the tour in French. The champagne will taste the same.
But a tip on the Mumm's tour: some tourists (I mean travelers) have not been able to do the tasting, because they didn't reserve the right tour. Yes, Mumm's apparently gives some tours that don't include tasting (if you can believe that).
And the OP will need to reserve the train ASAP.

I've posted this several times about Reims. Do not miss the WWII museum, which is housed next to the Ecole Roosevelt. It shows the war room as it was when the truce was signed there in Reims. It is very moving and well worth the trip. Of course, so is the champagne! There is also a small memorial to a Gestapo prison that is quite poignant.

I like the smaller cities' atmosphere and recommend a day trip to Reims on the train. You will enjoy it and appreciate the different atmosphere from Paris.

I'm so glad you mentioned the Musée de la Reddition, Pam S. I rarely see anyone talk about anything but the booze and the exceptional cathedral. We thoroughly enjoyed seeing the place where the surrender was signed as it was left 70 years ago this year.

Just Google Reims and explore what all there is to see and do in the area. I kinda like this link -- http://travel.michelin.com/web/destination/France-AlsaceLorraineChampagne-Rheims/news-ReimsArtDeco_capital. And this one -- http://www.francetravelplanner.com/go/champagne/reims/see/index.html.

BTW, right next to the cathedral is a Carnegie library in Art Deco style. According to our B&B host when we were there, most of the town was destroyed during WWI and rebuilt in that style. And yes, Carnegie did give it to the city, just like he paid for so many library buildings in the US.

I took the RS tour of eastern France in 2009 and my now husband and I are going back to take the same tour this year. It starts in Reims so this will be my second time there.

I definitely think its worth a day trip from Paris. The chalk champagne caves are fun to tour. We did a small family champagne house (Martel) and also Mumm and Tattainger. There are a few great Michelin starred restaurants in town too that are great to pair the regional cuisine and bubbles. The cathedral and architecture of the town are nice to see too. I am a foodie and wino so those were by far the main attraction for me.

Happy honeymooning! Great choice.

I love Reims! I loved the cathedral and the champagne, but also the rest of the city. I cannot wait to go back. As for the champagne, if you get tired of it (???), try the cidre.

I'm planning an overnight visit to Reims from Paris, also in April. Here are a few notes from my research.

Martel (recommended to me by a Parisian friend) has tours daily, open from 10 a.m. to 1 p.m., and from 2.00 p.m. to 7 p.m. The last tour begins at 5.30 p.m. The tour lasts about an hour (though they have a couple of different tours). You choose how many tastings, up to 3. A tasting is about 1/2 glass. According to google maps, it's a 15 minute walk from Pommery, and 20 minutes from the Cathedral. The website says booking in advance is advisable.

Pommery is a 35 minute walk from the Cathedral (or a 6 minute drive - take a taxi). It's also open daily. There are different tours. Book in advance.

Taittinger is a block or two from Martel (250 m.). Their website doesn't work.

Lanson was recommended to me by someone on the forum as a smaller house. The website is mostly in French. Lanson
You can book through the website. They are open Monday-Friday from 10-1 p.m., 2-7 p.m. It's about 30 minutes on foot (or a short taxi ride) , but not near the other houses or the Cathedral.

Mumm I combed through their website but could not find any prices. It's a 15 minute walk from the Museum of the Surrender mentioned above (Musee de la Reddition).

All the walking times are from Google maps.

Trains from Paris leave from Gare de l'Est. There are trains that go to Champagne-Ardenne where you transfer to the local TER train to Reims and trains that go to Reims-Ville. While it's more convenient to take the Reims-Ville train, it may fit your schedule better to take the Champagne-Ardenne train. Use this site https://www.capitainetrain.com/search/ to see schedules and book tickets.

I personally found Chartres to be much more wonderful than Rheims, also it is a much shorter train trip from Paris and is a smaller town so easier to walk around in. Note: like all small towns, you cannot lunch after 2 pm.

I spent a few days there a couple of years ago and really enjoyed the town. It had a nice feeling to it and we liked walking around the town and hanging out in cafes and the park. I was there in Nov., so obviously much quieter than Paris, but with so many days in Paris I think it would be a nice diversion.

If you're thinking of Reims then why not consider the quaint village of Epernay? This is where Dom Perignon discovered "stars" in his wine. It's also an easy day trip from Paris by train and the village is quieter....perhaps a nice change from the city.