Iv just done mine in Gun metal grey and I decided to keep the dimples on it, I didn't want it completely smooth as I think it looks $hit and doesn't suit the car but this is just my opinion. . . .
That's the good thing about Z's you can personalise them so much to each and every taste :-)
I only lightly rubbed it down and then primed and painted it, also iv kept the surrounds around the gauges in the standard silver to brake it up a little bit. . . . They are just glued in and need a little push to get the out. .
Really personalises your interior when it's done :-)