Well for a couple reasons I've changed my mind to a coupe now. I think they look better(wagons in a close second), stiffer chassis, lighter weight, they don't make them any more, and finally if I ever get crazy there are 22B kits out there(I doubt I'd ever spend that much on body work, but hey you never know). I'll probably get a '95 L or as close to it as I can simply because it'll be cheaper and the engine will be replaced anyway.
I decided against the BMW after looking into them more. Just searching through the BMW boards I found cases of the rear subframes ripping off, suspension mounting points snapping off and struts getting knocked through the strut tower. Things I have never heard of with Impreza's. With the Subaru, the only major problem I'd have to worry about is the tranny. Also there's that rally video to Linkin Park. Every time I start thinking about a RWD car I just have to watch that and realize it's AWD I want.
I don't know when I'm going to be swapping engines. I'd like to do it while I'm at school with the guard, but I doubt I'd have the time or tools. One thing's for sure, the drive up would be a lot more fun with an EJ20T in there. The L engine would save a lot of money on fuel though. So it will probably end up being next fall when I get back that I start doing engine work. I don't know about tearing the engine down. For starters I'll just swap it over stock until I get it refereed to pass emissions. I'll probably drive it like that until I get used to it and it starts to feel slow. After that, I don't know, I probably won't do anything crazy to it.