If your parents are interested in hitting up Vegas casinos, may I suggest Lake Tahoe instead?
http://en.wikipedia.org/wiki/Lake_TahoeThere are a ton of tour bus packages that leave from San Francisco to Tahoe, with stops at local casinos, and it's a MUCH shorter trip than Vegas (Las Vegas is an 8 hour drive versus the three for Tahoe). Also, even if they aren't interested in gambling, Lake Tahoe is
beautiful, so definitely worth a trip! You could probably find a great package for a nice holiday at Tahoe alone.
A great daytrip would be into Napa Valley for the wineries. Again, lots of tour bus companies offer trips to Napa, which is very good because you will definitely not be in a state to drive by the time you leave.
Once again, Napa Valley is very pretty. It's very reminiscent of Tuscany, so just the scenery alone is worth the visit!