Whomever said "the stock hood scoops and tmic arent really good past 60mph" more or less sounds like a retard. Otherwise why would Subaru engineer there 300hp cars to have them in the first place? They are very efficient and the only problems that ever occur really is heat soak from the turbo. But thats what heatshielding is for. So...discount what that person told you.
An STI intercooler is much more effective because it has a larger volume and more surface area to cool more air. In order to mate that up to your car, you'd need the STI Y-Pipe and definitely an STI Splitter (routes the air coming in from the scoop, over the TMIC) for the hoodscoop. An STI hoodscoop would be good to ensure you'd have a larger volume of air hitting the TMIC.
Hood scoops are virtually interchangeable over the model years and usually only need the proper splitters to line up. I don't think there will be much improvement from 02/03 scoops to 04+ from a WRX. Only the 04-05 STI scoops are larger...