I bought a G3 Intake. I'll probably do some form of Forced Induction at some point in the future. Was it worth it? Sure! It'll be a year, at least, before I would feel comfortable buying a FI kit - one, I want to wait for more competition and make a well informed selection, two, I want all the bugs and kinks to be worked out, three, since I have a 7AT, I want to wait until someone else blows their transmission, find out what boost levels they were running, and run 1PSI lower or somethin...
I think the same way...
The future isn't known (financial situations change, etc) - unless you've got 10-14K sitting in the bank to fund getting a TT setup NOW, then IMO, don't bother with it, either leave what you have in place, or get a nice exhaust that will give you some gains (and make your car sound/look better (those are subjective)) - FWIW, even if you toss the exhaust in the trash, you're talking about it being 1/10th the cost of putting in a TT kit...
I know but still, excess cost is excess cost...
Myself, I've got the exhaust on order, I've got a G3 intake. I plan on going after the LTH's from F.I. when they come out. If I'm happy with it then, so be it. If not, then I might look at some kind of forced induction...
I plan on doing the Injen Intakes, F.I. LTH if they are as good as we all know they will be, and F.I.'s CBE, just can't decide if I want CF or SS. I'm thinking CF since my Z will be black and I think it will compliment the CF look. 
Another thing to consider is, how often do you see a car that's half done? Some of them get referred to as "riced out" or whatever, but I bet those owners thought they had a good idea and went all out, but ran out of money, time, or had other committments that detracted from that project completion. I do agree with going all out, but, only if you have the means to do it up-front...
Well yeah thats what I plan to do, piece by piece get everything together, then once it's all in my possession, find out how much installation/labor/dyno/service costs are going to be affiliated, and once that's totalled save up for that. So that way I can do it all at once.. Figure pulling the engine out is something I don't wanna do often, so when I do go all out, do it once, and do it right so I don't have to again later...
Even then, I'm skeptical that 600WHP is achievable without spending a lot more on other components, not only to give the car some longevity, but also to actually make that power useful.