It will be new and fun times leveling in WotLK and with reset of entire server Economy. One of the things you will collect from 70-80 is lots and lots of green gear drop. The more stuff you kill the more of it you will tend to collect. What will you decide to do with all that green gear?
Well one the options if you so choose after picking up all that green gear is after you have a bit of a collection of it to have your guild Enchanter or a Enchanting friend DE it all for mats: Shards and Essences. Obviously you will need enchants to enchant your new rocking lvl 78+ gear and all those future 80 Blues and Epics. You don't want to be at the mercy of the AH trying to look for Essences and Shards at the beginning of WotLK or having to pay high prices.
They may not be any and if they are any you may be paying high prices for them. From 70-80 in Beta every piece of green gear I collected I had them just sent to an alt and latter when I found a good enchanter I just had him mass DE all of the gear and paid him in some the mats since he needed mats more than I did for his profession. I never had any problem getting any mats for any of my Beta gear to get it enchanted due to that. Hardest thing was finding a Enchanter that was skilled to do the enchanting since most weren't as leveled up as yet. So in all that lvl 71-80 gear I had collected quite a bit of the new WotLK mats in:
Small Dream Shard
Greater Cosmic Essence
Lesser Cosmic Essence
As well Planar Essence and Arcane Dust from all the 68-70 green gear that dropped in the starter zones as well. You may need the money and choose to sell or vendor the gear all up to you. But one idea is just to DE it all since your going to need new Enchanting mats anyway and quite a bit of it to look all shinny and glowing. Just a thought.