Based on my experience, here are the stuff I would suggest you to go for...
Go with low-poly style for graphics as these are the only ones that require little to no modelling skill and have low performance cost. 3D Rad doesn't give you the tools to make your graphics look good. You always have to get away with workarounds in order to get something that looks acceptable. For example, what I used to do is split my track models into 3 - 4 skinmeshes, so I can use a different shader on each. Bad idea as it definetly doesn't help 3D Rad's engine.
You definetly should spend some time on the UI. If you go with low-poly, UI wouldn't be such a problem for you. If you have enough knowledge in MS paint, then it's pretty much gonna work
. Just google "simplistic UI" or "minimalist UI" to get some ideas. They pretty much work in low-poly.
@nuskadamo, I have tried making a racing game with powerups. It does work, but as always: Performance sucks. This is due to inefficient usage of objects. It's just how 3D Rad is built. If you want to have each racer have 4 powerups (assuming that they require 4 objects), then for 6 racers you already have 24 objects. And ignoring performance cost, this is ridiculous to manage. Every time there is a bug, you have to replicate your code on 6 different places.
Decent car selection is somewhat possible. I recommend using the iObjectRefresh function instead of having each car have its own skinmesh. But decent track selection... Oh, boy...
Decent track selection requires you to multiply the already stacked replication that you have to do by the number of tracks you're gonna have. Simply because each track has to be its own project. Multiply that by the ridiculously slow loading of 3D Rad, and you're already frustrated enough to quit forever. What you can try is again utilize the iObjectRefresh for changing the track. Not sure how well it'll do for rigidbodies though.
For the AI, well... Not totally braindead, but remember that you're only exposed to a limited amount of external info. For example, it's not very possible to improve the AI's avoidance, because it would require 4 different scanner objects for each car.
Minimap is quite a simple one, but you can't mask parts of it. I assume it would be just fine though.
In conclusion... Question is: do you really want to create a racing game in 3D Rad? Are you willing to go through the frustration? If not, just don't waste your time and use Unity