My parents built a vacation home in Tahoe in the 70s, so I've spent a lot of time there! While Yosemite is worth a visit, I wouldn't take time away from Tahoe to drive there. There's so much to do in Tahoe, including outdoor activities, that I would stay there and do Yosemite on a separate trip.
Last summer, we took the Heavenly Gondolas to the top to see their new activity area. There's an alpine coaster (very fun!), zip lines, ropes courses, etc. You can also ride a ski lift to go even higher and see the view. There's a decent quick service restaurant up there too, so you can stay up there for several hours, do the activities, hike, have lunch, and ride the gondolas back down when you're ready.
The gondolas leave from Heavenly Village, which is a fun place to walk around. It's basically a big outdoor shopping area with fun shops (my favorite is called Up Shirt Creek) and restaurants. They have the only movie theater in South Tahoe. There's also an area that's a mini golf course in the summer and a skating rink in the winter.
If you like water sports, you can rent boats or jet skis on the lake. They also have boat tours (the MS Dixie is a fun one). Just over stateline, there's a riding stable. You can go with a guide who will take you up pretty high where you can great views of the lake. If you like hiking, there are tons of marked trails, some easy and some more difficult. My DH and DS did a hike last summer that took them about two hours to complete.
There are a few options for little day trips. You can get to Carson City in about 30-40 minutes. They have a fun little downtown area with some older-style casinos that are fun to see. From Carson City, you can get to Virginia City in another 20 minutes or so. It's an old-style western town that has been nicely preserved. You can also ride a train from Carson to Virginia City. Look up the Virginia Truckee Railroad for info. They also have a quick (around 40 minute) trip that goes from Virginia City to Gold Hill. The conductor points out the silver mines in the area and talks about what it was like to work in them. Virginia City also has some fun little restaurants (we like The Palace) and a few small casinos.
If you want to keep driving into Nevada, Reno is not much further. They have a bigger casino strip if you're into gambling. The Peppermill and the Atlantis are off the strip and both are fun.
Hope this gave you some ideas. Enjoy your trip!
