My God at the bad information in here....
The ONLY thing I agree with is the fact that you can't get your money back out of a car with H/C/I. But when did we start modding our cars to make money on the resale?
How much power do you want? There is nothing at all wrong with your car and it will be ALOT...wait let me say that again...
ALOT cheaper to mod than any 4.6L. Especially the 4v 4.6L which I would hope you would go for. And your ONLY option for making it fast would be mainly boost. You
can run them fast with nitrous but most don't.
Tell me your goal performance wise and I can give you step by step the cheapest way to get there given you can turn a wrench.