The quick way is to keep to the original colour,and matt varnish the car.highlight door edges etc.Re paint chrome parts the same way you paint plate armour.always paint the wheels,Personally I paint over the window glass as it always reminds you its a toy car.(also you don't have to strip it down to paint the seats).
For me not re varnishing in gloss is the way to go.Or a satin for a light shine.
But the big must for me is shade the gaps around a door,bonnet,etc.Its that little gap full of bright paint that shouts toy more than anything else.(Its a bit like display games where someone has half killed them selves to make beautiful buildings or spaceship corridoor's then paint it mono tone of under coat grey or sand brown.Without shading great work looses depth and falls flat.)
I hope that doesn't sound like a rant
