I am a pack rat and most of my assets in WoW are in Raw material form. Usually when I need cash, I may dip into those raw materials and liquidate them for gold, But with my 5 shaman team, liquid assets haven't been an issue for me at all with 1200-1500g a day income from dailies.

With that being said, Tradeskill income isnt really something that really pertains to multiboxers too much. Being able to simply go and farm instances for ourselves, we are never really too hard pressed with needing too much gold.

Most of the rich single boxers who are fairly affluent tend to invest heavily in tradeskills and peddle their wares in shattrath or ironforge pre bc. As most of the people who played Burning Crusade knows, the people who got their jewelcrafting up, regardless of how much money they invested, they made everything back in 20-30 folds. I expect the same results with WoTLK. Inscription, for the first half year or so, will net rediculous amounts of income and even more so if you have a rare recipe. This also pertains to tailoring for the cooldown cloths, alchemy for the transmutes, and possibly leatherworking.

So when the expansion comes out, everyone will be in a mad rush of sorts to either get character levels or tradeskill levels. Because no one will have actually gone out to Northrend yet, there will be 0 Northrend items to level tradeskills off of. This means everyone will be leveling their tradeskills of existing raw materials from Burning Crusade. Thus spiking the demand for said raw resources and increasing the prices. From previous experience from pre bc to bc, I would suggest unloading some of the raw materials you know will not be used in WoTLK before WoTLK comes out and holding unto the stuff you know will be used, and selling them after WoTLK comes out.

Some of the stuff that I have seen that will most likely be used are:
Adamantite
Heavy Knothide
Large Prismatics
Void Crystals
Pretty much all herbs
And to be on the safe side, I would suggest stocking up on at least a stack of all primals if you are planning to do tradeskills.


TLDR: Save all yo' shit foo.

edit: Large Brilliant prices sky rocketed early BC when people could not solo level 60 instances easily. I assume the same will be applicable if there is a recipe that requires a steady amount of large prismatic shards. Of course this is all in the short run. Prices will drop for everything Pre WoTLK because of the ease of farmability of said items, but until then, the short market is going to be very profitable. and in wow economy, the short market is really all that really matters because nothing is solid in the long run.