coilovers have only one advantage: They can be adjusted. If you plan to regularly adjust them for track conditions, they're invaluable. Seriously. Racing is about adjustments. If you plan on setting them and driving to work this month, to the grocery store a few times, go on vacation, go out on a date, etc without touching them every time your car starts up they're TERRIBLE. They have terrible ride quality, durability, value, and often paired with an otherwise fairly stock suspension system detract from your handling capability.
Oh, they do add value if you want your car to ride so low that you'd rather use your back as a shock absorber than the suspension. They work fine for that. So would a steel bar for a strut too, just don't ask a passenger to get in either.
2015 STi: Still Stock
04 STi, 04 WRX: SOLD