We've split our stays many times, usually between our 2 favorite resorts, Boardwalk and Poly. We're doing 4 nights at the Poly and 4 at BW again on Dec. 5.
It takes me about 10 minutes to unpack and maybe 20 min to pack, so that is not really an issue for us. I'm usually done packing before everybody is done with their showers in the morning. I have Bell Services bring up the car, pick up our luggage, put it in the car and drive to BW. Check-in at BW, get breakfast and we're off for the day. It is an early day as I like to check-in when switching resorts by 7:30.
Doing BW and Poly gives us the convenience of concentrating on MK & AK and MK resorts while at the Poly and concebtrating on Epcot, MGM and Epcot resorts while at the BW. We'll still visit Epcot and/or MGM while at the Poly and MK and/or AK while at BW, but this arrangement works for us.
steve