Of the three classic cabs that I have with metal panels and joysticks, all have CP art, one has no exposed bolts (Tron), one has exposed bolts for the joystick (Galaga) and one has exposed bolts to attach the underlying wood panel to which the joystick is attached (PacMan). My MVS-2-25 has exposed bolts to secure the CP overlay, but metal studs to secure the joystick. None of them have dustwashers above the panel.
I also have an OEM CapCom cab with a metal panel and no bolts for joysticks (metal studs), that does have the dustwashers above the panel.
Examples and Counter-Examples for everything will abound.
At the end of the day, Fozzy's statement stands and, for a scratch-built cab, it comes down to preference. I don't particularly prefer non-exposed over exposed, although I do typically prefer smaller-head bolts, if they are to be exposed.
For those who do choose exposed bolts, pr0k's bolt head restoration tutorial may be useful.
http://www.rgvac.com/restoration.asp?projid=17 