XFG - Ya. +1 for N/A 4WD.
RB4 - No. Old cars shouldn't be changed. People have learned to drive those and if devs changes the parameters, it would require more learning.
XRR - Why should GTR-car be more "driftable"?
FZ5 - Ever drived Porsche 911 without TC? If you have troubles taming it, use traction control.
UF1 - I like low-powered cars. -1 for adding more power to it. +1 to add another low-powered car.
XRT - Appearance is not what matters. You can add "agressiveness" by using "agressive" skins... Or if you would like to have bodykits and spoilers, use XRR.
FXO-XFR engine swap - You want XFR engine to FXO? Why? Because the appearance of FXO (But still want it more powerful)?
Water-temperature gauge - +1, after engine heat has been added.
Proper car damage - +1
Mesure fuel in liters - +/-0. Have been discussed on other thread.
All tires for all cars - -1. Why should you have slicks on road-car or threaded tyres for formula..?
Weather-effects - +1. Have been discussed on other thread (Multiple times).
More smoke - +/-0. It is only visual gfx-effect. I don't mind if it is added, but too much smoke would be too hollywoodish.
Headlights more effective - +1 after darkness is modelled. What do you mean by "more effective"? Currently, they don't have any effect.
Police-siren - -1. You can always change horn5.wav.