At the end of the day it comes down to your budget - if you can afford the £15k for a decent ed30, then you should go for it. They are more tuneable and come with what you want as standard i.e. colour coding.
If you start comparing the price of a 55 plate gti vs. an 07 plate ed30 then there's bound to be a difference in price, however if you compare like for like then it's not as much as you think, especially when you consider that the money you might spend tuning/customising a gti won't add any value, when it comes to resale.
HTH