msp's are fantastic cars for the money, they handle like no other car for the price, and yes they are not the fastest thing on the road but mine was definately not "slow". as with any car the mod fever starts to hit and things start to break, its just a matter of if you can afford to mod and fix a sub $10k car or a $20k+ car because either one you will be doing both modding.... and then fixing. as wagonbacker said, watch for the diff to blow, its a very common problem. also dont plan on boosting past 10psi unless you like large holes in your block or plan on going full forged and supporting tune
i.. bought a subaru because i can afford it and it's one hellofa car, but i still feel that my msp handled better even with FWD.... even with swaybar upgrades on the wrx. it's just the control in turns with awd that is decieving. until i went stage 2 on my wrx, the msp also felt faster because of the small turbo that spools insanely fast and some supporting mods that made my msp literally throw you back into the seat on boost.
subarus also have their problems, if you are not controlled enough to not dump the clutch you probably will blow up your trans. to boot, they burn clutches and have ring problems later on in life, but such is any performance car