Make that +3

The ED30 is a great car but will only keep it's value in the future if it is as close to standard as possible. If your thinking of keeping it standard, then go for the ED30 as it will be a great asset in the future.
If you are thinking of modding, stay with the GTI as I think the resale value won't be affected as much. Try getting getting a really high spec GTI and you'll have a great complete car. Anyway £2.5k gets you a complete K04 upgrade from awesome anyway.
Just my 2 pence opinion...
