common fact accessories dont add to the value in 2nd hand trade in.. so if you are going to do it I would suggest you find someone with 17" Denvers and take your 18"s off. Then when the Polo comes along, give the brand spankers to you new best friend and put the 18's on the Polo....
The assumption is that the Polo GTI is also borrowing from the Mk5 GTI parts bin.