Hi Phil and welcome!
I know LOTS of young couples that love Disneyworld! And I know you & your wife would enjoy each of the parks... for different reasons. As adults you could probably do each park in a long day, with the possible exception of Epcot (there is just so much to see).
Each park has several 'fast rides' or at least adventure rides, and a lot more to see and do that you would probably enjoy. Magic Kingdom has Space Mountain, Splash Mountain, & Thunder Mountain Railroad. Epcot has Mission Space, Test Track & Sorin. MGM has Rockin' Rollor Coaster & Tower of Terror. Animal Kingdom has Dinosaur, Primival Whirl and by March 2006 Expedition Everest. But there is SO much more... live shows parades, fireworks and lots of other fun things to do. My husband and I enjoy the parks as much as our 9 year old.
Do a little investigation on the WDW website on the attractions and ask questions on this board and you can get a pretty good idea of what specific rides you'll like and then go have a great time.
You mentioned Universal... we just got back from Florida and did Universal/Islands of Adventure in one day. There are rides but not much else. To me they seems almost barren compared to Disney parks.
It was just a few years ago we didn't think Disney was something we would enjoy that much. We thought we'd take our son once... but we loved it! And we've gone back twice a year ever since. It is one of the few places on earth where you can really forget there is a 'real world' out there and relax.
Do it! And don't wait 'til you have kids! There is a lot for adults that we haven't even gotten to enjoy yet... wonderful restaruants, and "Pleasure Island" filled with amazing clubs and fun just for adults!
Happy planning!