This may be a personal preference thing, but I would be bored staying at one resort for more than 4 days. If we go for a long weekend trip, we always stay at the BWV, but whenever we stay longer, we always split our stay between the Poly and the BWV.
First off, as I read earlier, you get to experience two different resorts. Every Disney resort is a vacation adventure in itself. By switching after 3-4 days, it's like starting a new vacation all over again. You feel refreshed and ready to go.
Switching over has never been a hassle. We always stay at the Poly first, and on our last day we wake up, drop our bags off with the luggage service, and DW, DS (14), DS (14), DD (2), and I head to the MK. Around lunchtime we take the monorails over to Epcot and have lunch there. Then walk out the back to the BW. Takes a few minutes to check in, and our bags are sent right to our room. We never really unpack everything anyway, so the luggage switch is no big deal.
While I would do it for all of the reasons I have already listed, the biggest reason that we swap resorts is because of transportation issues. We plan our itinerary around which resort we are staying at. While at the Poly we do MK, Hoop De Doo, and everything around that area. At the BWV we hit Epcot, MGM and DTD. This really minimizes travel time. The bus ride from the Poly to DTD is almost unbearable. By doing it the way we do, you can wake up really early, hit the parks, and then get back for a nap in minutes. To me time is money, especially at Disney. 30-45 minutes to wait for and then take a bus ride is too much wasted time.
Again, this is my opinion, and I am a very spontaneous person. I will wake up on any given day, and tell my wife we're leaving for Disney that afternoon. So swapping resorts for me is no issue at all. It's a preference thing. If you can't handle change and a little adventure, then it may not be for you.