Hey lads.
As already pointed out, the wrx spoiler is held with about 6 bolts and the sti is a whole lot more. I previously purchased a sti bootlid following accident damage to my wrx and it was covered in holes where the spoiler had been fitted. Far more than needed for the wrx spoiler.
If you dont want the hassle of drilling the bootlid or swapping the bootlid, check these guys out. As it's plastic, it only weighs 5kg, so may not need to touch boot springs? I'll be getting one when finances allow for my blobeye.
http://www.creativeauto.co.uk/epages/es144173.sf/en_GB/?ObjectPath=/Shops/es144173/Products/CA10070