Re: Should i learn another instrument?
The more you know about music, the more musical your playing will be. The more you know about harmony and arrangement, the easier it is to place musical fills in the song.
My parents made me take piano when I was 6 because they wanted me to learn a "real" instrument before they bought me a guitar. I picked up drums playing in bands when I was 12 and now that I'm burned out on guitar and spending my efforts on drums, some really good drummers have told me that being a musician first, and drummer second makes my playing much more enjoyable for them. They tell me that they would rather listen to a song with me playing than lots of folks with much more chops, because I have a feel for what makes the music move.
For a musical understanding, you can't beat keyboard/piano. Most harmony and theory classes are taught on that, regardless of what you're main instrument is. Most schooled musicians can play keyboard to some reasonable degree.
But if you're just looking to fool around with something to get an understanding of a different band instrument, I'd suggest the bass. Folks like Jordan and Drayton swap back and forth all the time. It takes a long time to learn all the harmony of a really good bass player, but learning how to groove with the drummer and support the upper register instruments is invaluable for someone who's primarily a drummer. When you go back to the drums, you're less conscious of how to blow chops and more aware of what the song is doing.