New tyres do that too, its to do with the PSI in them not the "newness".

Dunno about the MR shader, I never use them (or only very rarely) I would probably use a 2 blinns with a Mix 20 layer on it, just what I would prefer. Even if the MR shader has it you'll need to tune it to your material and how you want it to look.

I would be tempted to render it in a studio style set up, have a look at younglions car in the WIP, he put some set ups there that gives soem awesome results (down worry about the render times, its the quality you want at the end of the day)

Pain to add bits to the model eh?? Thats modeling some thing realistic for ya! The devil's in the detials and there the bits that really sell the model.

I think you've got the skills form the tuts you've done to have a crack at redoing the wheels and sorting out detials on the body etc etc.