That is some high mileage, but the price is actually decent. The book value is certainly a lot higher, even with mileage considered.
5MT Turbos are rare, and those engines will last a LONG time if cared for. Turbo rebuilds are cheap, usually US$150-400, and other nitpicky things occasionally go out, but all of the expensive parts tend to last a long time, and you can usually buy new, improved parts meant for the Impreza to replace what broke.
What kind of "racing" are you going to get into, autocrossing?