Geneva - Lausanne- Spiez-Murren- Geneva/Zurich

Switzerland is beautiful! I just returned from Lausanne & several Swiss cities & found Rick's Switzerland book to be less useful than some of his other books (that said, he does have a new one coming out, possibly before you go).

I've heard that Murren is lovely. If you are staying in hotels, your hotel will have a pass for that general area that covers local trains, buses, etc. If staying in private homes, you won't have that option. The Swiss pass covers many museums & tours, so that also may make it more economical to buy a Swiss Pass. The boat to Evian is covered for the Swiss pass from Lausanne.

Also, DON'T miss the Sauvabelin Tower (Lausanne). It's at the top of the hills & gives you 360* view of the area (& it's free!).

The audio tour @ Chateau de Chillon is worth it & the castles in Gruyeres & Aigle were also spectacular. In Geneva, the archaeological site at Ste. Pierre is well-worth the $ or (free on Swiss pass)--Audio tour too! The wine in Aigle was best-Chesselas varietal.

No need to dress up, IMO. I would say that the fondue is good but the rest of the meals were over-priced for what you get with exception of amazing breakfasts!

Can you arrive in Basel & depart from Geneve? Or vice versa?

Instead of back tracking I would fly out of Zurich.
Since train travel in Switzerland is most expensive a lot of people buy the Swiss Half Fare Card.
This gives you 50% off train fares and some mountain excursions. You only need to buy the Swiss Half Fare Card if you know that the combined costs of the pass, train tickets and mountain excursions will be less than the costs if you did not have the pass.

This site is some information on the passes and I'm certain that the Half Fare Card covers the lifts around Lauterbrunnen and Murren. But you have to double check.

https://www.myswissalps.com/swissrailpasses

I have never heard of a hotel in Murren or anywhere in the Lauterbrunnen valley that gave any kind of transportation pass. Transportation in that area is very expensive which is why some type of pass is nice to have. There will be a few changes with the 2018 version of the Swiss Travel Pass. It looks like it will include 100% of the fare up to the Schilthorn. My GUESS is that the swiss travel pass would probably be your best option, but the only way to know for sure is to do the math for all the trips you think you will do and add up the costs with the various passes.

I recommend you fly home from Zurich, and take the scenic train route from Interlaken Ost through Brienz to Luzern, where you change trains to go directly into the Zurich airport. This route passes numerous beautiful mountain lakes and waterfalls. And, as long as you're going this way, for your 20th anniversary, you could enjoy Giessbach Falls and GrandHotel Giessbach.
https://www.giessbach.ch/en/giessbach-falls-nature-park.html
To get there from Mürren, make your way back to Lauterbrunnen, and the train back to Interlaken Ost. Then take the train to Luzern from there that goes via Brienz. That train goes along bright blue-green Lake Brienz (Brienzersee) to the town of Brienz. Get off there and take the ship/ferry from there to Giessbach Falls. Coordinate your connection timing in advance by either asking at the train station or using the Swiss transportation app:
www.sbb.ch/en
When the ship stops at Giessbach, take the funicular from there up to the Grand Hotel Giessbach, a magnificent 100-year-old Victorian hotel with a fancy outdoor lunch terrace and short hiking trail up to different levels of the clear waterfalls. Or if you want a dressy experience, stay overnight at the hotel and dine in the super fancy restaurant inside.