I have all gold zelda cartridges except Alttp (would buy it in a heartbeat). To answer your question the gold AoL cartridge is not all that rare. If you're a collector (like me) then it's worth the 18$ assuming it comes with all the original promo stuff and box is in good condition.
Master Gamer est. 1987 Favorites Zelda, Street Fighter, Castlevania, Mortal Kombat, etc.
I've heard the golden NES cartridges were at first a limited edition, but they drew so much attention that Nintendo made it the standard so that they would sell more copies (thus the gray one becoming rarer). Can someone confirm this?