Hi! You probably already went on your trip - however I am just catching up with my AO emails LOL. I lived outside DC for a few months, several years ago.
An unusual Smithsonian museum can be found near the White House (which in itself is uncommon since most of them are not located there). It’s for glass art, and it’s a bit smaller than the typical museums so it’s very suitable for a short visit. If you like glass art you won’t be disappointed - it’s fascinating! I really enjoyed it.
I also concur with other folks about the Dupont Circle neighborhood - it’s very walkable and it’s fun seeing all the embassies! There is a cupcake shop with lovely treats. From what I remember, in the warmer months there is also a farmers market however it may not be open in the winter.
I also personally enjoyed walking from Dupont Circle to Georgetown and from there I would walk past all the shops in that affluent neighborhood until I reached the Francis Scott Key bridge which will take you into VA.
The views at night from that bridge are spectacular (they’re nice in the daytime too, of course). You see, DC is odd in that it has no skyscrapers (no buildings are permitted to be higher than the Washington Monument) - however the neighboring town across the river is Rosslyn which has a couple of typical city skyscrapers. (Rosslyn is also a nice little city to visit and AO has an article on its metro station.)
So at night as you cross into VA, there are interesting views if you take a full 360. Straight ahead are the bright lights of the tall buildings, to the left you can see the city in the distance with the Washington Monument towering over the rest of the national capital, behind you the warm lights of the Georgetown shops and local community, and to the right… darkness! To that side of the Potomac the river stretches much farther and the wooded land beside the river is undeveloped because it’s part of the George Washington Memorial Parkway (which is a lovely drive if you have time! It takes you to multiple parks).
In fact if you ever find all the monuments and museums a bit too mentally tedious, DC has a ton of nice city parks and green spaces. Sometimes it hardly feels like a city!
As far as over-rated attractions, personally for me the Newseum did not hold any fascination at all, but it’s quite popular so I may be in the minority!
Hope you enjoy your trip. DC is a nice little city with things to do for all ages and interests.