Haven't been playing quite as long, but I'm in the similar situation as you. My advice is to read as much as you can on the DiscGolfReview site, and spend some time reading through the technique forums on this. Within in the last couple months I've pretty much abandoned my old throwing techniques and have been starting from scratch to get a good form developed.
I've basically based my form off the Rick Bay's Driving Form & Technique
article. I also eliminated my X-Step for awhile, and worked on smoothing my throw out, pulling the disc across my chest, follow through, grip etc. When I find a problem I'm having, I read the Repair Articles, check the forums, and then post a question if I'm still having problems. I'm amazed how willing people are to help you out on this site, and receive great replies from folks that have been where we are out and have made it to the next plateau or so.
There is also some great discussion on disc selection. I learned very soon that I was throwing discs I'm not ready for, and changed my bag a little bit. I know I have taken some steps backwards in hope of gaining a few more steps forward. I'm not throwing where I want to be yet, but I have seen more improvement in the last month or so than I have in the last couple of years.