Okay, hot off the presses: using the "Perform" option from the Songs menu for a single song only changes the scenery. Performing a song as part of a set seems both to kick up the phrase levels and also level easier. I just did both types of performance, and there were clear differences.
Oh, and don't play "Space Ostrich" at the end of the session when your reflexes are starting to slow and your fingers hurt. Ain't. Gonna. Happen.