Kawaguchi vs Extra Day in Tokyo for National Museum?

We have a very short trip to Japan (3.5 days). It’s our first time. Since the trip is short, we’re spending the full time on Tokyo. I’ve done a fair bit of research and read the FAQ, etc., but I’m torn between spending one of our days taking the bus to Kawaguchi, doing the boat ride, walking the lake etc., OR we could spend an additional day in Tokyo seeing some specialty museums–probably will start and spend most of the time at the National Museum but if we have time we may do the coffee museum, railway museum, samurai museum, etc. My question for you all – is Kawaguchi a “must see” even if it means missing a precious day to explore Tokyo and it’s amazing museums? Obviously they are both great but I’m asking about the tradeoff–if you only could do one, which would it be?

Some context – We land on a Sunday at 3PM, then fly out Thursday early AM. We are there 12/11-12/15. I love museums and history, but my wife isn’t as keen (if the museum is just okay she’ll get bored after two hours). She’ll be 5-months pregnant so want to be mindful of too much walking. We know it’s cold at the lake so will pack heavy jackets.

More context in case helpful – Proposed itinerary:

* Day 0 – Get settled into the hotel and overcome jet lag. Eat near hotel in Kinshicho

* Day 1 (first full day, Monday) – Either Kawaguchi bus, lake walk, boat ride OR musem day in Tokyo. See above.

* Day 2 – Hired a GoWithGuide to do a bunch of the main sites: Imperial Palace bridge, Tsukiji outer market, Ueno Park, Sensoni Temple, Meoji JingunShrine, Shibuya Crossing, Hachiko statue. There are umpteen posts about these well-known sites and a whole FAQ about it, so for brevity I will avoid elaborating. We feel good about this itinerary.

* Day 3 – teamLab Planets at 10AM, sunset at Shibuya Sky (I’ve already made a reservation at The Roof), then spend the rest of the day shopping in Shinjuku, Harajuku, Akhihabara

* Day 4 – Fly out

EDIT: I tried to elaborate as much as possible so this isn’t a low effort post. Hope this works for the moderators and is better than before. Thank you!