personally, if you can get the car for free with a good title and all the parts, get it. Then do one of the following three things:
1) sell it on Craigs list or other venue
2) junk it. many people will pay you atleast $100 to pick it up and junk it for you
3) parts it, then junk the shell. There are several little things that you could remove and sell, then junk the rest
Now, with the money you get from this you can either buy a winter car (not really practical. See below) or you can save it and pay for a car wash once or twice a week to keep the SSEi clean in the winter.
As for not practical, you remember that ontop of the purchase price, you also have to pay for title, registration and insurance for the new car, as well as insurance still for the SSEi. Also, if you don't have a garage available, there really is no reason to store the car. It is still out in the elements, just stationary allowing the elements to chill out on it. If your state uses salt, then yes, it would be away from this, but if it is parked near where other cars are, the salt from them will still be near. Atleast with driving it, you'll be able to wash it regularly.
Just some thoughts from a guy who stores his bonneville in the winter.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4