I think this has been covered before, well I think it was similar, something like do you regret getting the sp model and not the nismo instead something like that.
But as far as your concern goes, I would say that is what mods are for. I mean I have seen a sports package model changed to a Nismo with OEM parts. Only thing that most people cant really change is their transmission. Although I bet there is a way to do that too.
But since their isnt a thread exactly like this one, might as well make a new one with a poll. As for me wouldn't change a thing, color, specs, model, year, LOVE my Z!