If you go for new bonnet you can always revert to standard if you decide to sell and recover some money separately for the one with a scoop.
You are looking about £90 for the scoop and about £200 for a bonnet
http://www.ebay.com/itm/New-Hood-Front-Panel-Primered-Subaru-Impreza-2007-2006-SU1230139-57229FE121-/231052250061?fits=Make%3ASubaru|Model%3AImpreza