Why should you go to a gaming convention? The first and most obvious reason is to get out of the basement (kidding!). Conventions are great ways to network, get some new ideas for games, and buy a ton of things you didn't know you wanted until you saw it. When D&D 4.0 first came out, our group went to a con to check out a demo and talk to folks who were playing it already (we then unanimously agreed to boycott it).
You can try new systems, games and even genres. I never knew I liked cooperative board gaming until I tried it at a convention. Most gaming cons also have war gaming rooms set up so you can ooh and aah over other gamers prized scenery and skill at terrain building and mini painting (and maybe show off your own).
The main reason I go, though, is for the merchandise. I live in a place where gaming gear is hard to come by, so going to a convention is pretty much like walking into paradise. It's always fun to see the newest accessories for your gaming table and bring them home to your group. We've acquired magnetic bases colored for different spell effects, spell radius grids, and a host of other little gadgets that we now use pretty constantly.
If you're really brave, you can even host your own sessions and have the chance to play with some new folks! So don't be shy--you might even enjoy it.