Stay away from Great America. That place is NO fun. That's all I really remember from Sunnyvale. Why not take a trip to San Francisco while you're so close. That's all sorts of fun.
If you have a car, I'd say drive down 17 to santa cruz and check out those little beach towns. The Boardwalk can be lots of fun, they have a special i think on thursdays where you can turn in a Pepsi can and get unlimited rides after 5PM (something to that extent). We would just hang out at the beach all day and then hit up the boardwalk rides at night. The rides are pretty old and not very thrilling, we would just go on the Giant Dipper over and over.
Yea, Santa Cruz is a very cool, old surf town. It's a great place to visit and the boardwalk is definitely a fun place to hang out. Agreed, many of the rides there are mediocre, but the Giant Dipper (one of, if not, the last original wooden roller coasters) is still a lot of fun.
But the beaces there are great, the town still has that hippy, surfer vibe and there are cool coastal towns all up and down the coast from there.