"Jack, I've spoken on many occasions previously but I was never in Toastmasters."

If you're planning to be speaking for money, Toastmasters might be a good investment. I would recommend at least checking it out to see what you could get out of it. Since you are not a beginner, you should check out 'advanced' clubs.

With public speaking, there's nothing like experience. TM allows you to practice in a friendly environment where you can try new approaches (doesn't matter if they fail), and to benefit from the knowledge of a group of people who have been doing this for a while and should be able to give you more useful feedback than most other groups.

You can also use the club as a way to practice for media appearances (tv interviews, radio, etc).