Is there any benefit to running 12V instead of 9V?

For our reverb/echo/chorus effects, the only difference is an extra 2.5 dB of dry-signal headroom. That's imperceptible in most situations, though it can help in a line-level effects loop. For our other effects, there's no advantage to 12V at all. One firm rule: never power these pedals with more than 12V. There's some protection against higher voltages, but sustained over-voltage can cause damage.