I think it comes down more to the options than the engine. If you want a car with all the bells and whistles, your SE will cost what a stripped down RT will. If you're more in it for the motor than the accessories, go for a stripped down RT (which is what I have and love).

As for weather, I'm damn lucky enough to be able to keep mine off the road in snow, but my wife has a Wagnum, same size, weight, frame as the Challenger, so handling should be near identical, and we use that year round here in Chicago. As long as you get the traction control/ESP option, generally speaking, I'd say go for it. The grocery-getter handles just fine through about any weather we've thrown at it the last 2 winters, including a few times even I wouldn've rather had my Wrangler, but it always came through.

-Rench