Well I have bee to DL in June and August. WDW in July. No comparison. DL is much less crowded in the summer and it is not muggy so the heat is much easier to deal with. This upcoming summer you might find a large wave of crowds at DCA because of the opening of Toy Story Midway Mania. But lines for other major attractions shouldn't have lines more than 60 minutes even around peak times, assuming weekdays. I think you should spend at least 4 days considering none of you have visited in a while or at all. Preferably 5.
Here's a list of rides unique to DL that you don't want to miss:
Indiana Jones (ride vehicles like Dinosaur, much better themed with an amazing que line)
Pirate's Lair (Tom Sawyer Island with a pirate theme, lots of pirate caves to explore, a pirate show, CMs dressed up as pirates just wandering the island, plus a Captain Jack Sparrow meet & greet)
Pinocchio (Fantasyland dark ride *a little scary)
Alice in Wonderland (Fantasyland dark ride)
Mr. Toad's Wild Ride (Fantasyland dark ride *a little scary)
Roger Rabbit's Cartoon Spin (Spinning Toontown dark ride)
Matterhorn (1st ever tubular steel coaster)
Casey Jr. Circus Train and Storybookland Canal Boats (gentle rides through Storybookland. Good for kids)
Everything at DCA except Soarin, ToT, Muppets and Bug movies, and Turtle Talk
Rides that are significantly different:
Jungle Cruise (different jokes, some different scenes)
PotC (much longer and better)
Pooh (no long lines at DL because it's tucked away in the corner, different ride vehicle)
Splash (different seating, shorter ride, not as long lines as MK except during summer)
IASW (original version)
Tiki Room (original version)
Autopia vs. TIS (actually has scenery and stuff to look at, you even go off roading)
Buzz (removable guns make for easier aiming)
Space (completely dark, and smoother with music)
ToT (different scenes, no 4th dimension room)