I really don't think rooms are assigned ahead of time. I was at Beach Club on points two years ago. I had my requests. The CM checking me in said they had a room available with my requests (Epcot view). As we are talking, he looks back down at his computer and then says (seriously) "oops, while we were talking just now someone else checking in TOOK your room that I was going to give you."
That's right - someone else checking in while we were standing there, got assigned my room. I ended up getting a pool view (which was great in the end) and had to wait 3 hours for it to be cleaned.
I seriously don't think rooms are preassigned if they are assigned, cash and points don't matter.