I used to swop professions often. You will find once you it max skill with any profession that there always seems to be a reason that another profession is better.
So I changed strategy.
I now have all the professions covered by alts and they are all on skill 450 except leatherworking which im leveling with my druid alt and its on 380 atm. Just make sure that mining and herbalism is on a character with epic flying mount and you can fly in Northrend. Using this method I never to level up a profession from scratch again. The downside is that you probably wont get the BOP epic plans/patterns that drop in lvl 80 dungeons, but then thats a good reason to spend more time on that character to get the character into those dungeons.
This has worked well for me. I can enchant just about any enchant. I have access to all the decent gems. I can transmute when needed. I dont buy any flasks, haste potions etc. Saves me a fortune keeping my main gem'd, enchanted and high on flask

I am always fully stocked on enchanting mats, cause all my BoE greens and blues goes to my enchanter to de. I always have at least 15 flasks in my bag. I try to keep a stock of 5 of each epic raw gem and about 40 of each herb that often use. I sell the rest which easily covers any emergency outlays and basically funds the flying skills for my alts.
My main is a warrior who does herbalism and enchanting. I recently switched from tanking to dps, so I am thing of dropping the herbalism in favor of skinning, but I need to compensate and get herbalism on another alt is qualified to fly in Northrend.
Occasionally I need to buy the odd gem, but by doing the Dalaran JC dailies im getting all the JC patterns. I have most now to cover spell power, stamina, strength, expertise, intellect. etc.
EDIT. i have also found, by just doing the lvl 80 dailies for an hour or so with my gathering characters, that I always get enough ores and motes(or whatever the Northrend version is called) and herbs to keep the crafting professions going.