Whoever told you springs and Oem shocks are better than midrange coilovers probably didn’t know what they’re talking about, with the weight of the Z not really being on its side it’s fair to consider that updating the suspension will change the car drastically- it all depends on your budget and application- 800+ is where I’d roughly say the lower limit is for these cars and dependant on the manufacturer ie meister, hsd, teon, yellow speed brc are all in this price range- do your research and compare to what you think you can afford