For an O'fest Ale I would look to make a malty amber ale then spice it in the secondary.
I find that most pumpkin spice recipes recommend too much spice. I'd cut back by 1/3 or so and give it time to meld before tasting. If you think it needs more you can always add it.
If you overspice you can blend it with almost any other beer out there to thin out the flavor a bit without thinning out the brew.
Correcting overspicing can also get you some good results. You can split the batch in half and blend one half with a lighter brew (pale ale) and the other half with a stout. Go lightly on the stouts as the roasted grain may overtake the flavor of the spices. I would probably mix the 1/2 batch with about 1 pitcher of the other beer to blend in. For stouts I'd recommend closer to 1 pint to start.
I've made Pumpkin brews in the past and while they were tasty, I'll never make another (at least that's what I keep telling myself)...