Hmm, I'm not sure? Should I try something different?
When I move the ground of the 7805 to the ground output of the PSU, the analog pot readings go wild again. It's pretty rock solid going off the 9v and ground of the wall wart though.
I do know the centered PSU did clean up the noise in the audio signal. So while the ground config may negate some of the intended benefits of the PSU, it is accomplishing the primary goal of getting rid of the noise in the guitar audio signal.