That sounds awesome! However, bar Florida and a couple of European parks I don't have much experience of Theme Parks. I'd definitely recommend PortAventura (ideally on a weekday out of the school holidays)
Flights to Reus are fairly cheap (Ryanair fly there) and a day, given that the park is open from 10am - midnight in the Summer, should cover it. There's also a beach nearby and Barcelona can be reached on a bus in about 1hr and 30mins for 19 euros.
Alton Towers, Animal Kingdom (WDW), Blizard Beach (WDW), Chessington World of Adventures, Epcot (WDW), Hollywood Studios (WDW), Legoland, Magic Kingdom (WDW), PortAventura, Seaworld (Orlando), Thorpe Park, Typhoon Lagoon (WDW), Universal Studios and Universal Islands of Adventure