I've also been shooting causally for more than a decade. I've also had thoughts about going pro. You may be good, but there are also many people out there who are at least as good as you. And don't say competing with fellow pros. Nowadays, with DSLRs and pirated copies of Photoshop CS2, the market is flooded with wannabe freelancers, some of whom can be quite good. They can afford to undercut everybody else without guilt.
How about a transition phase? Keep your dayjob, shoot on the side. Then see how. That's my personal plan anyway. This kind of business thing, a lot of it depends on luck and timing.
This kind of thing, don't anyhow rush. I also damn sick (as in really damn sian) of my job, but in this age of economic uncertainty, I really appreciate the stability. But like someone said, you won't know if you don't try. Then again, you have to be pragmatic also. If you're the sole breadwiner and/or putting food on the table to feed your family is a priority, then sorry, reality bites, keep your dayjob. HOWEVER, If you're young, single and living with your parents and/or you've got a very supportive spouse who's willing to support you financially, then you could give it a go.
All the best in your decision.