Gold allows you to play multiplayer. Basically, silver is a cheap way to make you feel good. "Oh, Microsoft is so cool giving me a free silver account", but it is only a way to talk to friends, at that point, not very useful.
I definitely suggest getting Gold because for $50 you can keep playing games that you would be bored of very quickly. (ie FPS games)
But i have a lot of riends on 360. I also already got it. I already mastered the PS3. I really want to play 360. Yes or no? Do I "HAVE" to get Gold Membership? And is it $50 for a month?