x2 or whatever on Letchworth SP and Watkins Glen and the Corning Glass Museum. One could very easily spend a few days at Letchworth State Park; it's a quite large park, several miles long.
If you like amusement parks even a little, Knoebels should be on your list; it's a first-rate traditional park and having an adjoining campground is very convenient. (The campground itself is clean and well-kept and well-run, but otherwise ordinary; some of the sites are quite tight.)
Philadelphia does have lots and lots to see. The art institute is fantastic, even if you don't care to re-enact the scene from Rocky. Hershey has some interesting sights, as well, particularly if you like chocolate.