There is usually an event, the Bob Marley Birthday Bash, at MXIII for a fee. You can do a google search and see what's being promoted. Usually some smaller events hosted around the beach from what I recall. I'd also keep an ear on Wavz beach, the Negril beach park, and Woodstock seems to be promoting larger events with their expansion.
I would also just ask around when I arrive and see what's going on. Don't worry about buying "tickets" to any events prior to arrival. In other words, don't stress about it. But it is fun to see what might be going on while you are in town!
I would definitely say that there are people who travel specifically to JA for the 6th, but it's busy season anyway, so busy regardless. Bob wasn't known to spend too much time in the Negril area so I don't think there's as big a draw compared to, say, Kingston.
Others may know more or have a different opinion!
Have fun!
