I just got back from Yosemite Valley, where I helped chaperone a bunch of 8th graders attending a NatureBridge session.
A highlight and physically-demanding day, took a bus around 8am to Glacier Point and walked down from there. Take lunch and two quarts of water (1 1/2 will leave you just a bit thirsty).
The folks who took the Panorama Trail past Liberty Dome, Nevada Falls and Vernal Falls (if you can handle the 8 miles) got back around 5:30pm but had a great time, or the "4 mile trail" if you are interested in a shorter trip. When I was younger I hiked up and down the Panorama trail and have to vote for "downhill" hiking as the way it should be done. This time I took "4-mile" as it was my assigned duty... It was fine, great views of Sentinel rock... and Yosemite Falls from a distance.
Camp Curry (now Half Dome Village marked on signs but not the maps) serves good meals in their dining compound. The coffee corner is open at 6am, serves Peets and the baristas are great, and the pizza is good and they have good beer on tap.
Check sunrise and get yourself up before twilight breaks. Your friends will likely still be asleep and you still have time to get back to the coffee corner and bring them coffee just as they awake and name you "hero of the day". The sky changes fast and you will be well-served if you get out before the dawning sky brings your contrast range to N-2 territory. (I have a shot that would have been better taken of the Merced with Half-Dome in the background... if I had gotten there just as twilight broke.
Yosemite Falls will be brutally touristy. As will all the pull-outs.
The best day by far, was when we walked from a spot near El Capitan... up "Old Pine Flat Road" where we got a view similar to the tunnel view, but without people and with an old dirt road for foreground. Makes you feel like you are there in 1850.
From there we lunched under El Cap, and continued back to Camp... Half Dome Village, along the less-populated trails and across the meadow... we hopped the shuttle back. Being West of "everything" and across from the views, we had very few other people on the trails with us.
Another day they took us back behind the kennels where there's an apple orchard. From there we went to "split rock" and the pounding rock there. I loved the unusual places they took us. There's this place called the "Spider Caves" where, if you are not too corpulent, and if you are not claustrophobic, you can make your way through on your back and side, crawling like a spider (not that there's spiders in the cave but you crawl like a spider to get through them).