Well you have the beginning of the Food & Wine festival at Epcot, the beginning of the Mickey Not So Very Scary Halloween Parties, PLUS the end of the Free Dining Promotion all happening at that time.
Other than that, I haven't a clue. (snark)
Sorry, though, that you can't extend your stay one more night. I'm sure THIS might be a pain in the caboose, but have you thought about splitting up your stay in more than one resort? If you were going from a 7 night to 8 night stay, try 4 nights in the Contemp. and 4 nights in one of the other resorts. I think Disney even takes care of moving your bags from resort to resort, so you can just check out on the way to the parks on Switch Day, and then just mosey over to Resort 2 when you're through.
Of course, I've no idea how packed the rest of the resorts will be, for the same reasons listed above.