I've never really thought about "priorities" as such, so if others say something is "low priority" they are not officially speaking for me (although they are usually about right!)
Really I have only one rule: to make the best Pokemon site for information about the games. But if I had to tie down some priorities, I'd say it goes like this:
High Priority: Anything that breaks the site completely, like pages not loading or any major error. Also whenever a new game comes out, I try to get the key information on the site asap (new Pokemon, moves etc). In other words, this is the stuff that I make time for.
Medium Priority: Any incorrect information, like Nightmare saying "Special" instead of "Status" :D (BTW I just fixed this). I try to fix things from the minor errors thread or errors that are emailed to me as often as I can, but life/work tends to get in the way.
Low Priority: New additions that are not mentioned above. Generally, anything that doesn't make the site worse by not having it. Stuff from here I'll typically do when I can find the time, or if I'm in the mood for it.