I'm kind of with Matt on doing Niagara Falls in a day. It really is very tourist trap-like. I think 4 days there is overkill BIG time.
Too bad on being vetoed on Henry Ford...I've never been but from folks I know it sounds fantastic!
I'd do a couple of days at Gettysburg at least. Take a ghost tour (10 yo should love that), tour the battlegrounds and the visitors center. Have ice cream at the Cannonball Malt Shop.
X2 on Knoebels. It's a unique in that they have a lot of rides bought from amusement parks that have gone out of business. It's very family oriented, won't break the bank and you won't wait 90 minutes for a ride. They have their own campground but are others in the area as they fill up.
Check out Steamtown in Scranton. There's also a coal mine in Scranton you can tour.
Lancaster area is very nice but may be a bit boring for a 10 yo. If you're into it, Sight and Sound is excellent.