Looking for Suggestions For Things To Do Before River Cruise

The Jungfrau is too far from Luzern to do as a day trip. You have already said "Murren but it looks like it will take a half day from Lucerne", but getting to the summit of Jungfrau is even further.
Instead I suggest Titlis: http://www.titlis.ch/en This is a mountain with a small Glacier at the top. You take a train from Luzern to Engelberg, then a series of cable cars to the summit.
I would also keep your plans fluid. There is no point going up a mountain if the top is in cloud. Look at the weather forecast daily, and if the next day is clear get up early and do Titlis or wherever.

The train route from Luzern to the Berner Oberland (Interlaken etc.) is pretty, it runs over the Brünig Pass.

You could split your trip, 2 nights in Luzern (boat trip + Titlis), then take the train to Mürren (over the Brünig Pass) for 2 nights, and go direct from Mürren to Basel. That is if your luggage will allow it!

Basel is worth at least ½day, but you said no cities.

You can investigate train times and prices at the SBB (Swiss Railways) site: http://www.sbb.ch/en/home.html
You may want to consider either a half price card or a Swiss pass for this trip. You can look up prices on the SBB site, and do the calculations.

I always like to plan routes with a map. The Swiss Railways official map is here: https://www.swisspasses.com/railpass/overviewmap_en.pdf

Traveling with luggage for an 8 day cruise? Is that different from traveling with luggage for a 2 week non-cruise vacation?

You say you want to see mountains, lakes scenery and no cities/museums and you also want to see the Jungfrau. My plan would be to get on the train in Zurich Airport and head to the Lauterbrunnen Valley (at the base of Murren). Spend your time there until it's time to go to Basel which is only 3 hours from Murren (a very do-able train ride). You'll see lakes, mountains, waterfalls, stunning scenery, ride a gondola, etc. You can also do the Jungfrau from there if you must see that, but I would rather recommend the Schilthorn which is much closer and much cheaper. You might opt for neither once you arrive into Murren and see the stunning surroundings.

If you want 2 spots, go to Muerren directly from the airport. Spend at least 2 nights. If you want to put Luzern in the mix, then take the Bruenig pass route to Luzern. Luzern is just a bit more than 1 hour from Basel.
Anyway, you have lots of choices.

Thank you all so much for your recommendations. I sense a common thread and that is to go to Murren (or Lauterbrunnen) directly from the airport. I am now going to look in to how long that will take and how easy to get there from Zurich. We have decided to ship our luggage for the cruise and will be travelling "light". My concern about luggage is now out of the equation. Since we have a direct flight from ATL I suspect we will be arriving around 8AM in Zurich. By the time we clear customs I'm thinking we will be on a train NLT 11 or noon.

And then we will double back and spend 2 night in Lucerne. Does that seem reasonable?

Thank you again.

Day 1. Arrive Zurich. To Luzern (2nts)
Day 2. Mt Pilatus and lake
Day 3. To Lauterbrunnen (3nts)
Day 4. Jungfraujoch
Day 5. Murren
Day 6. To Basel via Bern for river cruise

If you are arriving at Zurich at 8 am, my experience (5 arrivals or so) is you will be on the street at 9 am. You could be on your way to Muerren at 9:40 am, after buying tickets and getting to the platform. You'll be wandering the streets of Muerren at 1 pm.

It's very easy to get from the Zurich Airport to Murren via Interlaken Ost. With as few as 1 connection from Zurich airport to Interlaken Ost you'll have a peaceful ride - especially without your bulky luggage. Before you hop on the train purchase some snacks for the 2 hour ride to Interlaken Ost. We love the wine and cheese snacks although you may traveling a bit early for wine :-)

After you get to Interlaken Ost is where you'll get on a small train to Lauterbrunnen. Then in Lauterbrunnen you'll walk through the well labelled tunnel paths to the gondola for a 5 minute breathtaking beautiful ride to Grutschalp where you'll walk 15 feet and board the "little train that could" all the way to Murren. Sit on the left side (facing forward) for the best uninhibited views. Murren is stunning.

Whether we go to Murren or Lucerne first it sounds like it will all be wonderful. One more thing - recommendations for hotels/ B&Bs please.

Thank you

Hotel Staubach in Lauterbrunnen has great reasonable
accomodations, great views and you can get everywhere
reasonably fast.

Thank you all for your recommendations. Wish we were going sooner!