1. There's lots of people who drive their M3 in the winter... STi certainly isn't lower than that. If any car in this performance class can handle winter, you've got to count the STi as one of the best suited.
2. You can already get both winter tires and ASA wheels that fit from www.tirerack.com,
for a total of about $1200 USD plus shipping.
3. All the new cars with painted with water based solvents have the same issues with paint chips. That's why you install paint protection film. If you think you're immune to paint chips during summer think again.
If it were my choice, I wouldn't do it. If I can't come up with the extra $5000, even if it means saving another year, then I can't afford the car, which means being in a bad situation if your finances change for any reason. For example I wanted to help my two closest family out and having the M3 didn't leave a lot left over for me to help them financially as much as I wanted to, so I eventually sold it.
The other thing is that after buying a car so early in the model lifespan, I learned a few things the hard way. Reliability / Production issues, i.e. e46 M3 engine issues, and features, namely SMG II, which was made available less than 2 months after I got my car.
Now certainly you can get caught up in the waiting game, there is always a new feature or next neat thing or style to have. Arguably, the best, most featured, and most reliable version of any model run is the last year. You can see this time and time again if you pick up a Lemon Aid guide. But, the last year of a model run is usually just a year or two away from the next version, which is "better" still.
But on the other hand, if you don't have the money to buy the car outright, and not owe anyone anything afterwards except maybe gas, tires, insurance, and tickets, then there's no harm in waiting a little longer, provided you already have reliable transportation.
I know for many people, myself included, taking the STi out in the winter isn't exactly the first choice. Heck, summer or winter, who doesn't flip when you get that first parking lot ding? But even if you don't worry about the small stuff, you always wonder about that other idiot in the SUV going full bore who learns SUVs are great at going fast in snow / ice but not so great at stopping.
At any rate, I'm sure the guys who do put snow tires on are going to have a lot of fun this winter.