Speaking as someone who currently still owns a classic Impreza, they tend to suffer a bit from understeer in standard form, but that can be overcome with thicker ARB, ALK and decent suspension. The early classics have shocking brakes, the later ones come with 4 pots up front which are better but still not wonderful for the track - upgrades are readily available but can get very pricey (can easily match the cost of the car in certain cases). The upside is you'd be lucky to find a standard classic these days; it'd actually be easier to find one with most, if not all, the track prep done already.
Unless you go for a scoob with DCCD