Since it seems like a lot of the time, when I look for help on here, the threads leave you hanging on whether or not a problem actually got resolved, I wanted to confirm that deleting the W3TC rules from the .htaccess file WORKS.
I did the same thing, adding user agent groups to W3TC and gave myself the 500 Internal Server Error. I also tried deleting the folders for wptouch and W3TC on the backend, and it didn’t work. So I put everything back and ONLY removed the lines in the .htaccess file.
Worked like a charm!
Now I just have to go clean up my mess.