Doesn't sound too far off to me. The Z is pretty efficient NA. You'll have to spend a lot of money to get anything remotely noticeable in terms of power increase. I'm well over $10K in mods with about 10% hp increase from stock
Also, why do numbers even matter? How does the car drive? Do you enjoy it?
If the answer is no, you should sell it and get another car that fulfills your needs. Let someone else who might actually appreciate your car enjoy it
