Lauterbrunnen is a 14 minute train ride from Wengen and is the main transportation hub for everything you're going to be doing while in Wengen. In 5 nights of staying in Wengen you'll likely go through Lauterbrunnen 4 or 5 times to get to places you want to see, so it's not going to be something new and exciting for you at that point. Plus, what's beautiful about it is the Lauterbrunnen VALLEY, not the actual town of Lauterbrunnen where the hotels are, which is a mess of day trip bumper to bumper car traffic and pedestrians crowding the sidewalks so much that you literally can barely walk on them without getting pushed out into the street. It's not charming and you can easily experience the beautiful part, the valley, from Wengen without moving there.
Personally, I'd be staying all 7 nights in Wengen with easy day trips to the region without having to pack up and move. But, if you do want to move, Murren is very lovely and a special place. You could save all your activities for that side and from Wengen focus on Wengen/Lauterbrunnen Valley/Grindelwald and a day trip to one of the lakes. In Murren, nice hotel options are Murren Palace, Hotel Edelweiss, Hotel Eiger & Hotel Alpenblick.
Another option is to stay on one of the lakes for a completely different experience. There are some beautiful spa hotels like Beatus Wellness & Spa Hotel right on Lake Thun, which would be a lovely and relaxing 40th anniversary spot. The boat stops right there at the hotel so you can go out on the lake to explore different villages along the lake, as well as the 3 castles on the lake (Spiez, Oberhofen & Thun). It's an all inclusive hotel, so it would be a really relaxing place to just enjoy the lake and take some relaxing boat rides to the different castles after spending 5 days doing more active day tripping from Wengen.
https://www.beatus.ch/en
