I was a fire/EMS dispatcher at a VERY busy dispatch center for five years. The shift I was a part of was home to some of the best dispatchers I've ever known, and I have been around for my young age.
I'll tell you this: going into the job, having volley fire/EMS experience CAN be very helpful, BUT, when you are just getting started, FORGET EVERYTHING YOU KNOW!!! No matter how much you're sure that you "know a better way," you MUST follow the DISPATCH procedures, which may contradict what your past field experience tells you.
Then, once you get some time under your belt, and begin to develop a rapport with other dispatchers on your shift, as well as the field providers you service, you can begin to integrate your DISPATCH knowledge and your FIELD knowledge and make the most of both.
It's not the glory job you're expecting going in. Remember, on any normal night, or week, or month, you'll have to muddle through hundreds of "my belly hurts for five days" calls to get to that one "MY HOUSE IS IN FIRE!!!" call, or through hundreds of "my neighbor stole my parking spot" calls to get to the "armed robbery in progress" call.
It is a great job -- a fun job -- and it's what you make of it. I'd still be doing it if the center I worked for treated their employees more like people and less like luke-warm bodies filling the chairs!