Everything Michael said above is accurate. You're on an enthusiast forum where people come to find information and advice on modifying their cars. This is not something that is WRX specific. There are endless number of sites for enthusiasts of all different kinds of cars. I would be willing to bet that just about everyone here who modifies their WRX, would still be doing mods if they have had chosen a different "sporty" car, whether that be a Porsche, an Audi or a Civic. My last car was an RSX, and the ClubRSX forum was just as full of people modding their cars as this one is. The difference being that in my experience, the WRX is a hell of a lot cheaper/easier to modify, especially in regards to increasing power.
To reiterate the point on Summer tires...they are just not meant for Winter driving. Doesn't matter what vehicle they're on. You have a few options here. Buy Winter tires, swap them on and off your stock wheels when the time comes each season, buy a 2nd cheap set of wheels for them, or just get a set of all season tires. I'm almost positive you could get the dealer to swap out the Summer tires for a set of reasonably priced All Seasons, and then you can go about your merry way driving on those year round. That being said, nothing will beat the cold/snow performance of dedicated winter tires. I bought my WRX at the end of January and had Winter tires shipped to the dealer and mounted on my stock wheels. This was my first time ever having winter tires, and when combined with Subaru's Symmetrical AWD, it was absolute pure awesomeness.
I don't know where you're from because I don't see a location listed under your name, but if you are looking for AWD, I'd LOVE to see you find a better car that's more fun to drive for less money. Even if you could find an Audi for the same amount of money, you'd probably get wrecked in the rear when it comes to maintenance and cost of ownership. I really wanted an A3 when I first started looking, but you can't even get one with Quattro and a manual gearbox, not to mention it still would have been more expensive than my WRX.
I went with a base because I didn't feel the need to spend the extra money on leather, fogs, and a sunroof. My RSX had all of those, but I don't really miss them. If anything, I only wish I had the heated seats/mirrors/wiper area. More importantly to me, I didn't want want the spoiler that comes with the premium/limited, but that's just personal preference.
Your comment about them looking "small" makes no sense to me, especially since you said you saw an STI that looked like "a good size". Other than the wing, the body size/shape is identical. Maybe it WAS due to the fact that they weren't in the showroom and you hopped out of an Xterra. Take the wing and badges off of an STI and most non-enthusiasts won't be able to tell the difference from the outside (brakes are about the only other visual cue). For me, the size of the sedan is more than enough. I can drop one of the seat backs down, put my hockey sticks and pads through the opening, then fit my giant bag full of equipment in the trunk, and STILL be able to drive myself and 2 people around comfortably.
If you think the new widebody WRX looks like a Civic, that's your opinion and I don't intend to try and argue about it.
Bottom-line, if you haven't test driven one yet, then we are probably wasting our breath. I fell in love during my test drive, and couldn't be happier with my choice (ok, so I DO wish I could have gotten an STI, but we're talking $26k vs $40k+).
PS - If you're looking for something bigger and "nicer" with AWD below or around $30k, you might want to check out the Legacy.