My 1970 280 has also had a colour change from pale green / biscuit interior, to Navy ( Duncan ) blue / biscuit interior. It looks great and I wouldn't have bought it if it had been green, in fact the reason it was sprayed was because it wasn't shifting in green ( also easier to hide some of the rusty bits I suspect ). Red doesn't sell in the UK either for some reason although I know it's popular in the US.
If you are going to enjoy the car, I would have it done, but as Kgear pointed out, its probably a good idea to have it done in a correct colour. As far as value goes I would relax, it's not going to halve the cars value is it? and if you can afford a good full respray ( about £15K in the UK ), the couple of grand value hit (if there was one) shouldn't matter.
Go on..treat yourself.
paulr