The biggest thing I have learned so far is that great capture = easier mixing. I often find myself opening tracks you send out and saying "why can't my acoustic (or other instrument) sound like that". So what I am hoping for is a lesson/feedback module that will see you rate tracks we capture by how use-able they are in the eyes of a pro mixer like yourself. Perhaps it could be in the form of a Feeback Friday type event once and a while where you dissect a session (with a reasonable track count and information on how it was recorded and what was recorded) that PLAPA members captured to critique how each element sounds and give us honest opinion on how 'mixable' the track is would be great. Heck, I think I would go so far as to pay for a service like this as an add-on as I know it could be relatively time consuming to bring up a session to critique.
Anyhow, this might be a little 'pie-in-the-sky', but hey, if I don't ask I'll never know!