Leather makes a big difference on resale, i found it very hard selling my car and finally Craig bought it on here and got a very good deal. £16k for a 2004 zed with only 17k miles on the clock. Bloody cheek!
If you go for the non-GT, i would suggest getting a leather retrim as that is all that people seem to want. However if you intend on keeping the car a long time, go for the non-GT also.
L