I've seen some of the 80ish blues in WOTLK firsthand in the beta auction house, and if you have T6 stuff you won't be buying most of that stuff. It's good, but generally the problem with the gear I saw in the AH was that it wasn't balanced well. Like you might see a jaw-dropping DPS plate item, but it'd have no stamina at all, just pure DPS. I think that people who maxed out on BC will be okay to keep their stuff until 80 and begin gearing up in 80 dungeons with a lot of T6 type stuff still on.

The thing to keep in mind with WoW itemization is that high end PVP or PVE gear usually has a mix of stats that can't be replaced simply with higher item level. You won't get high resilience/stam gear from regular quests.