The one thing I've found so far in the beta, considering the prof's have not been updated as of yet, is the lack of world drops. Meaning the mats you get leveling, or from quests, such as greens to disenchant or various other base mats used by the profession, aren't dropping from killing. Granted, this is the beta so alot of things that will come up/drop in the live version simply have not been implemented as of yet.
With that said, and considering this "expansion" -- as you said -- is more of a revamp of old content, I would think that holding on to older stuff -- for your Goblin's and Worgen's -- is wise to an extent. I'm not saying to stock your GB with nothing but old mats/gear and etc, but keep some of it. Everyone's gonna wanna to at least try a Goblin or a Worgen, and with that will come the professions, so having some of those mats handy will only benefit your guildies.
Personally, as I have several "guild banks" that I own personally on the live servers, I'm having my guildies mail that stuff to me for storage for the time being. I'm leveling a Goblin and a Worgen and making note of the things I need -- as I've leveled all but Engineering to 450 on live -- and having them stock pile the basics. My guildies are happy to do it, and in the end if the prof's update to the point that we won't need those things once Cata is live, then there's always the option to sell. Granted we won't get as much, but still...every copper helps.