Having a pro work with me to establish consistent, repeatable form is what worked for me. I shot on again, off again, for 20 years, like you describe, before I signed on for lessons with Rick Welch. Though my accuracy has improved a lot, I still miss. The difference is that now I have a pretty good idea of why I miss, and if I shoot another shot that corrects it, I know why I missed.
I know people are probably getting tired of a few of us constantly talking about Rick Welch, and I would imagine that there are others who could teach you just as well. Rod Jenkins comes to mind. Although I haven't had lessons from him, I have been impressed by his video, MBB III.
I suppose the ideal time for me to have had lessons from a pro would have been about 18 years ago; if I had, maybe I would be competing against Rick in the IBO. But what the heck, I did a lot of other fun things during those 18 years, and making a leap forward is fun whenever it happens.