I have only been to WDW once on our honeymoon in Sept '06 (hurricane season) so I am far from being a WDW Vet. I remember it being hot and the sudden rain storms (10-45 mins) that occurred during our week long stay.
However, the rain felt so good and as a bonus it cleared the parks. We literally were walking on rides (although the air-conditioned dark rides were a bit rough). We always had ziplocs for our electronics with us and flip-flops in our backpacks.
If you are able to brave the rain, you may be able to accomplish alot AND beat the heat at the same time.