It's worth the trip for sure, but it is a lot of driving. You could see the mariposa grove and the valley OR tulomne meadows, but I wouldn't try both or you will driving all the time. In the valley, you could do one small hike. The hike to vernal falls is amazing, but really the best part is the end when you get to vernal falls, and it is slippery at the end. You could hike to the footbridge and see the falls. I don't know how full they are this year, given the drought. Mirror lake is always an easy option - last year there was no water in August, so do check that out. It's still a pretty hike, though. You can check out lower yosemite falls, which is an easy walk. Again, don't expect a lot of water this year, especially in the summer, but my kids enjoy scrambling on the rocks in that area (not near the water, which is dangerous, but on the way there).
"Friendship is born at that moment when one person says to another, "What? You, too? I thought I was the only one." C.S. Lewis