I personally would use Etching Primer then the colour required and lacquer if required. What's your plans Mate ??
They make plastic primers specifically for this.http://cgi.ebay.co.uk/VHT-WHITE-PLASTIC-PRIMER-PAINT_W0QQitemZ110460012220QQcmdZViewItembut why spray when you could flock ... http://cgi.ebay.co.uk/Race-Rally-DIY-Dashboard-Flock-Kit-/170538083224?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item27b4dca398
Never tried it, but looks super cool