V8 STi is a V7 STi with exterior facelift, Thunderbird 2 rear wing, V7 RA Spec C cams and twin scroll headers + VF37, hypereutectic alloy (rather than forged) pistons, new (and still ugly) steering wheel, softer wider seats.
V9 STi is a V8 STi with new stronger 5x114 hubs, wider rims, Spec C front suspension arms and geometry changes, facelifted interior, yaw sensing diff setup.
IMHO the one to get is a V8 STi Spec C if you want a blobeye. I wouldn't go for a plain V8 STi, as the V7 RA Spec C is a much better car from a performance standpoint (and you get used to the bugeye!). If you're not prepared to live with a Spec C and want more comfort/amenities, then I'd agree that for a bit more money the V9 STi is the way to go.