1) Community. I've made quite a few good friends through Subaru clubs, that I never would've met had I not showed an interest in the boards.
2) Money spent. Initial purchase price, routine maintenance, and insurance is expensive enough, but being an enthusiast has you always tweaking and adding/replacing parts. That (along with what breaks because of added parts) adds up.
3) Only time my car has been undrivable is when I sheared off a bolt in a caliper support bracket. I have to take better care of my driveway than I would if I had an SUV in winter time, due to the nature of a car having lower COG, but I didn't help the situation with the RCE Black springs I threw on.
4) You can save money buying used, but you can also buy someone elses headache. If you can afford to buy new, that may save you some piece of mind. Your call. If you buy used, you want one that has been maintained properly and never modified (beware of pre-sale part outs).
5) I have never had an issue with the interior of the car. You have to remember, this is a tweaked version of an entry-level economy vehicle, so you don't have the luxuries of other vehicles in a similar price range. Things look/feel cheap, there will be random squeaks and rattles, etc. Go in knowing what you're paying for, or else you'll end up disappointed.
6) I've attended about a dozen meets that required driving 500+ miles in a day. I've driven to/from FL. I've never really had an issue with my car I wouldn't have had in any other vehicle.
7) Know what you're buying with a WRX. You're paying for a more capable version of an economy vehicle. It will have a similar build quality to a $15K car, at a $25K+ price tag. It will have odd noises, it will have its quirks, but it will be a fun ride. If you're looking for a reasonably-priced vehicle that can put a stupid grin on your face when you get on the throttle, the WRX is a great option.