I've only prestiged once in CoD4. Thats because I got bored really fast when I first reached 55. I prestiged and a week later I'm back at 55.
At around level 40 I came across a mystical golden Ak47. I never seen one before. I thought it would look stupid but it looked marvelous. I thought to myself "I've gotta have one". I've been at level 55 for a while. I would get one paint job at a time for each rifle. I made sure not to get bored of any weapon. As a side project I worked on getting the golden shotgun. I easily got that. It required way less headshots.
I rarely come across golden weapons in the game, unless I dropped the golden shotgun myself. I guess its up to the player if he wants to prestige over and over again or earn the golden weapons. I can tell you now, just leveling up is wayyy easier than getting 150 headshots with each weapon just to get that bling bling.
I'm getting really close to getting the golden AK47. About 3 more weapons to go. Hmmm, then what? Golden UZI.
Or if you're really hardcore you could go to max prestige and then get the golden weapons. Meh, who cares. Its just a little symbol next to your name.