You are most likely getting the majority of these errors while being in capital cities, especially near vendors.
I suggest you save at a different inkeeper, clear the contents of your Cache folder periodically and, if needed, use vendors in other cities to purchase your gear.
For example: I get alot fewer errors if I'm saved and hang out most of the time in Thunder Bluff, then I do in Orgrimmar. Try doing the same for a while with your characters, depending on your faction.
Good luck!