Its fun to do as a challenge, to prove you can do it to yourself, etc. However, don't bother doing it for (1) loot, (2) gold. Northrend is far, far, far superior in terms of itemization and gold/hour to anything you will do in TBC at level 80.

I myself run first boss Kara and ZG once a week just to farm mounts, already have one horsemen mount and one tiger mount drop. I like doing it and its fun for me. Sometimes i do onyxia, again for the fun and challenge not for the gold. But in 1 hour of doing Sons of Hodir dailies, which not only gives lots of gold but ALSO rep towards necessary shoulder enchants, I make 94g + drops (got a number of rares, greens, etc) in 30-45 mins doing 6-7 daily hodir quests, per character, or 500g total. Its even higher for multiboxer friendly dailies like the ebon hold, warsong, etc but I'm mostly focused on Hodir until I hit exalted. I've also collected 300+ relic of ulduars, which I can use for rep after next patch or probably sell for 1000g+.