What are your opinions on performance mods?
Personally I am not a big fan of modifying GTAV's cars' engines because they ruin the feel of the car, one of the best things about AdrenalineX is that we don't care how fast the car goes: we even race trucks and utility vehicles (whereas everyone starts moaning in GTA:O if you choose anything other than 'Super' or 'Sport'
). We could have some races which allow performance mods, but only a few.
I am a fan of the cosmetic personalisation, and although they do affect handling it would be good to give people a choice of wheels and suspensions:
Suspensions do affect handling but it is a trade-off: a lower car does not roll, but it handles bumps less well.
Wheels do not affect grip or handling, but it has been proven by NODO that off-road tyres jump over kerbs better (so we may want to restrict wheel type at the choice of the author, e.g. "In this race you are only allowed muscle wheels").
As for car choices, I think today's SA:MP AX offers the best balance: everyone racing the same car, or two evenly-matched cars, or SK race. GTA:O is way too restricted in its car choices because although you can choose classes, every class has one or two obvious leaders making all the other cars go to waste.
I think it would be great if we saved preferences to a database so each person can customise their car to their liking. That way you can choose "This is what I want my Banshee to look like when I do a Banshee race" and the game will load that preference for you. Maybe we could have a /garage world where people can go and configure their builds.