DO IT!!
My parents took my brother and me out almost every year when we were younger for trips in October. We always go assigments ahead of time (though whether we actually worked on them during vacation or not I cannot remember). And let me tell you something...those family memories are more precious than anything I would have been learning in school those weeks.
And those are the vacations we remember the most. Summer trips to Disney are just not the Disney trips we remember. September/October vacations allowed us more "family" time to enjoy each other's company and spend "Quality" time together.
My boyfriend on the other hand...his mom, dad, and 2 brothers are teachers. They are appalled by the idea of taking kids out. I even remember going for a choir trip to Disney in high school (a school choir trip) and some of the teachers were just down right abnoxious about missing school for such a thing. Never will understand that.
But you are the parent and as a child who was pulled out every year for years and years...take the kid out and have an AMAZING vacation! Those memories last forever. And take LOTS of pics!