I Haven't got a MiniZ, but i know there's a lot of mods available to them, tires susp.. check your local dealer, they should be able to get you the parts you want.
I've got 3 mini Z's. I got one for Christmas a few years ago (castrol mugen NSX). My brother wanted one so we could race so he bought an Original Teile Mercedes. He later bought a Mini Z F1 McLaren. We found a shop that sold cheap Mini Z shells so these are the body's we have:
Xanavi JGTC GTR
R34 GTR gunmetal
Sprinter Trueno
Castrol Mugen NSX
Original Teile Merc touring car
D2 Merc Touring car
Evo VI Rally car
Subaru WRX Rally car
Altezza yellow
McLaren F1
We made a track out of our 6 Taekwondo competition matts. Crazy fun that was...
If your looking to get a Mini Z make sure you get a MR-02 model. The ones that I have are MR-01's which are still good but the MR-02 recently came out with many changes such as better 'to scale' models, motors and suspension.