October can be the luck of the draw. We followed up a WDW trip with a couple nights at VB last October (23rd - 25th), and it was great. The air temps were increasing all along that week to where it was in the 80s by the time we got to VB (so great park weather transitioned into great beach weather for us). We just missed the turtle nesting, but we spent a LOT of time in the ocean. The temp was a little cool at first (I think it was marked in the upper 70s on the board??), but once in the water was fine - and I'm a sissy in cold water.
Compare that to Nov08 and we caught the cold front. We still got in the ocean (DD8 was going in regardless), but it was chilly.