We do it all the time now. Being DVC members, we most often split stays between VWL and BCV. If we need to pay cash for a few nights we split between WL or BC and the Poly.
We love it. It's like having two vacations in one. We don't have a problem with the switch since we live out of our suitcases on vacation anyway (so packing isn't a big deal) and we always have a car and move the bags ourselves, so the transfer is easy.
It's nice to split between a MK resort and an Epcot resort. That way you can plan a lot of MK time, with easy access, while you are at the WL......and plan a lot of Epcot/MGM time, with easy access, while you are at the BC. So that's what I'd do, WL and BC. In fact, that's what we are doing after Thanksgiving.