You should keep in mind that heroics/instance don't take anywhere near as long in WOTLK as they did in BC. Infact with a good group in BETA I was generally running a full Heroic every 30-40 mins no problem. Alot less trash in zones. Also raiding is less consumable dependent, as well as faction/rep grinding not being as much of a PITA as it was in BC.

IMHO Blizzard did a good job at making the game require less time to invest while making it more fun overall. It will still require time, just not as much as before.