Welcome to the community, Alex!
To answer your first question, yes, there is great potential in the 370Z. Just keep in mind that going FI is the easiest way to acquire large gains. As far as a tuning package goes, Cobb should have their access port available for the 370Z soon. People that use the access port have seen decent gains N/A, but like I said, if you want big gains you will have to go FI.
Anyway, that Mazdaspeed 3 looks sharp! I am sure you will not have any issues selling it.