Not the lose money chessnut. !!!
Your car (mARK 5 GTi), will be worth no less when the Mark 6 comes out, there is not a massive drop as people think there is.
It just does not happen, the reason are this.
When a new car is Launched you get some people that must have the latest car to hit the road, and can afford to buy it.
But for your average joe they cant, so they opt for the best of the rest your Mark 5 Gti.
Also when the Mark 5 was Launched, i had people every day saying i dont like it, i'll never buy one of those.
I dont know you, i dont know where you are getting your car, but it will have no effect ( other than normal depreciation), on the currant Mark 5 price.
Stick with it, and remember as of yet there is no Date for the Mark 6, what if its two years away.