If you do put your GT4 up for sale I would sell all the mods separately, one of only 76 in this colour, that is if all originals still survive.
I saw it at the wales weekend and thought it was one of the best GT4 examples i have seen.
You will want a premium price for the GT4 on it's own, i don't think that you will get the true value of the mods in addition to this.
I hope you decide to keep her.