Ahh the hype, any car can have any value. BMW can worth more than a STi or the STi can worth more than a Bimmer, it's all to the buyer and what he's willing to pay. About the mileage on a car, actually the most stressful time on the engine is actually cold-starting, not really how many mileages are on the engine. Cold starting is when all the parts in the engine doesn't have to the most adequate lubrication = most wear on the engine, so an engine with frequent cold start can actually wear out the engine faster than a high mileage engine.
And back 2 the subject of the STi vs. MSP, well STi pushes like a fat kid rolling thru mud. Don't know what people's obession with AWD, it's nice and safe, but it ain't the best way to race. First, you loss the most out of all drivetrain configuration (FWD, AWD, RWD) due to more components in the drivetrain. Plus AWD aren't good for racing, cuz it doesn't let you turn, hence the safety factor of all wheel drive. Now I'm talking about track racing, not considering off-road racing. The only way STi is more performance than MSP is cuz it got more power so the car accelerate faster, but that doesn't make it a better car. Car with less HP can and did beat it, i.e. EVO. So with that in mind, give me 31k, and a choice between STi and a MSP: I'll pick MSP, cuz the money save goes into MSP's engine and the STi will have a handful against a now more capable MSP.