I'm going to go off the beaten path and say tires.
One of the best improvements you can make, especially in Maine, is separate winter and summer tires. I've heard arguments that performance all seasons are fine, but in Maine I'd personally rather have two sets of tires. Some of the scoobs come with RE92's and they're terrible. Tires are the thing that connects your car to the road, so all the power and suspension isn't going to do jack if you're tires suck.
After tires I say suspension then power.