With just 3 days in Wengen, I’m not sure how practical it will be to
try to fit Murren in. Just getting there and back will take a good
part of the day.
Wengen - Mürren is 43 minutes.
Doesn't make sense to hit Grindelwald from there with your very short
stay.
Wengen - Grindelwald 54 minutes.
I am not sure that people realise just how different it is to visit this area in the beginning of March compared with July or August. If they did perhaps their advice would be different.
In Wengen and Mürren you can expect the streets to be covered in snow - it is possible to ski or sled on the streets in these car-free villages, so they do not plough them. You definitely need to be thinking of winter conditions, even to just walk to the store or train station from your hotel.
If you are not skiing or doing other winter sports (there are some wonderful winter hiking trails), then you will have a lot of time to travel around to the various villages in the area. With it taking less than on hour to go to either Mürren or Grindelwald, I don’t see why you would not do that. To come all this way and remain only in Wengen makes no sense to me.
In your various itineraries you talk about visiting Thun or Bern - yes! Do that. Every year I enjoy all of the spring flowers in these cities. Thun is especially enjoyable as you are able to view the snow covered mountains in the distance while not having to be in winter conditions yourself (in general - you could of course hit a spring snowfall there as well, weather being what it is).
Also, I have to disagree with the idea that Wengen is somehow “more Swiss” than Lausanne. They’re just different sides of Switzerland, not more or less authentic.
Lausanne is very much Swiss. Even though it’s French-speaking, Swiss-French culture is not the same as France. The city shows everyday Swiss life — how people live, work, study, and govern — which is something you won’t get in Paris or Strasbourg.
Wengen and Mürren are beautiful, but they are small resort villages. These villages are heavily tourism-focused, and English is heard everywhere, particularly in hotels, restaurants, and transit, with a large percentage of the visitors coming from the U.S. Most Swiss people don’t live in places like this, and the experience there is shaped mainly around short-term visitors.
Switzerland isn’t one single culture. It’s a small country made up of different regions and languages — French, German, Italian, and Romansh — each with its own traditions and way of life. Visiting only alpine resort towns gives you one slice of Switzerland, but cities like Lausanne show another equally Swiss part of the country.