At first, I didn't understand the draw of the split stay either, but then . . .
1) Our boys are antsy and like to be on-the-move - same for my husband. Switching resorts is a way to do that.
2) We love old favorites, but want to try new resorts. As previous posters mentioned, the split stay allows us to do that.
3) We've had APs in recent years and will get them again. Because we're visiting WDW more frequently, we're spending more time at our resort than we did before. As a previous poster also mentioned, the resort is a big part of the vacation for us now, so it's fun to have a variety of resort experiences in a single trip.
4) We've become increasingly appreciative of easy transportation in WDW. Epcot resorts allow us to walk to dinner almost every night. MK resorts offer quick access to MK in the morning. A split stay allows us to take advantage of the location benefits of each.
5) There are five people in our family with very strong opinions about lots of things - including Disney. We really like to take everyone's preferences into account when planning vacations and selecting resorts, and the split stay allows us to do that.
6) With the frequent visits, we need to show my husband that there really is something new to see/do at WDW. Split stays help to mix it up and introduce him to something new on every trip. (And new ADRs help, too!)
We're frequently on the move during our vacations (just drove from San Franciso to Newport and stayed in 4 different places within a week - and drove hundreds of miles in between!) So handing our luggage over to Bell Services, going about our day and ending our day in a different place with our luggage delivered isn't a problem.
And starbox, our plan for February 2013 is six resorts in six nights! (See my signature, below!)