Here's a list of really good reasons to come to DL.
1. It's the only Disney them park that Walt Disney was ever at. He oversaw the construction, spent a lot of time there, and even slept there. While he did have a big part of the initial design of MK in WDW, he wasn't around to oversee the construction.
2. DL is charming, much more so than MK. The fact that it is smaller makes it seem cozier.
3. In most cases, for the attractions that both have, DL's versions are superior, especially Pirates of the Carribean and Space Mountain. The only attractions I give MK tops on are Splash Mountain and Big Thunder. Otherwise, DL gets the nods.
4. DL has more attractions than MK. Add DCA into the mix, and you've got about the same amount as all 4 WDW parks combined.
5. Better entertainers. Way better entertainers (therefore, better shows). DL has a much larger talent pool to draw from, therefore, all the entertainment CMs actually have talent--they can sing, play instruments, are great comedians, can act, etc... While at WDW, at many shows only one or two of the performers are actually wearing microphones, at DL they ALL do. DCA's Aladdin has performers from Broadway.
6. Summers aren't so humid (it very rarely rains during the summer, so, no need for ponchos unless you just don't want to get wet on the water rides). Yes, it gets hot, but if you're used to humidity, it won't seem bad at all to you.
Hope that's enough to convince you.