The one time I did a split stay, I just took a taxi and moved my luggage myself - Cost about 12.00 and I just had Bell Services hold the luggage since my room wasn't ready.
I much prefer to know where my luggage is and I'm tired of waiting hours for Disney to get it to me when I use their services. I will use RAC when I check out but will no longer use DME when I fly in. They have taken too long to get my luggage to me (4+ hours from check in at resort) the last 2 times. and I'm not trusting Disney to move my luggage from resort to resort.
I would think it would be the same issue moving from resort to resort - you'd be without your luggage for hours while they are moving it.