The San Diego beach idea isn't horrible - she can sit on the beach and the kids and run around and play in the water.

Yellowstone can be OK - there's a lot to see that isn't too far from the roads, but there's also a lot of hikes if you want to do that. Just have to decide how much time you want to spend sitting in a car and/or if she's OK sitting and waiting for you and the kids at a trailhead.

I'd consider Tahoe. Nice in the summer - hit the beach and let the kids play while she can sit and chill.

Anything you're interested in seeing that is a car drive? The Grand Canyon? Mount Rushmore? I know the North Rim of the Grand Canyon is something you can get to without much walking, but a bunch of driving. I'd be thinking of stuff like that - you think it would be cool to see, the kids can hike around a bit if they like, but your wife might be OK sitting and watching.