What do golden verhicles do for you, except cost a lot of money? So far I've only upgraded Mr. Snuggles (or whatever the dragon is called) to gold, and the only difference that I noted besides the golden color was, that it now reaches more into the screen which actually makes it harder to use, since you have less time to spot zappers coming at you?!
Other than the fact that you get to ride shinier vehicles, there is a secret achievement that is unlocked when you purchase your first gold vehicle (which you've already done). Its called Blinged Out.
Gold vehicles should be no different from the regular ones.
The Golden vehicles are no different aside from the visual effects (they are reflective gold all over and sparkle a bit). There's no functional difference, the only practical use is to get an achievement (at least I believe there was an achievement for buying one of them).
They shouldn't take up more of the screen either though, They're just re-skinned.