I shot my first IDPA match in December with the 1911 Colt Commander I own. It was a real blast, both literally and figuratively. If you use your 1911, then you will shoot in CDP class with others using the same thing, so you do not need to worry about competing with the high-capacity 9s, etc.
Even if you want to shoot a revolver, there's a class for you to shoot in, as long as it has a 4" or less barrel. Revolvers in .38, .357, .44 Special/Mag, and .45 ACP/LC can all be used.
No matter what you choose, even if it's bullseye shooting, I think that you'll find acceptance from the others.
As to buying a new gun first, that's your choice. Who am I to discourage someone from getting another pistol...heh, heh. But you may want to shoot a couple matches first to get an idea what class you want to shoot in and get a feel for what guns seem to work best for what you choose. That's what I am doing.