I don't have any advice for you about avoiding crowds, sorry! That's the nature of the beast. We've been in June, July, August, a 4 day weekend in early December (not on points), 4 days at the end of December, and spring break (not on points either).
We are doing spring break this year on points and it is really silly. We just bought (again) in March, so we have the 07 and 08 points, and we are using all of them and paying one weekend night in cash. Now if we had gotten a 1BR instead of a 2BR we would have just used points, but my kids are older and I think a 2BR is better for us.
Unless your schools take a break in a non-busy time (I know some places have a fall break, but we don't) you just have to adjust to heat and/or crowds. Weekend trips suck up the points.
I can tell you the heat was the worst in August of the summer trips we've taken, and crowds were "best" mid July after the 4th crowds were gone.
Robin M.