the lower the kickup the more agressive the steering will be but it won't handle well on bumpy surfaces that's why they are using this on carpet since these tracks are normally very smooth and normally shorter and much tighter than outdoor tracks so you want the more agressive steering response.
As far as low rollcenter goes, the car initiates the turns better and tends to carry more cornerspeed this way.
I don't know the answer to question #2.
Dremel tool #408 Sanding Band 60 grit works very well.