I have yet to have found a single need for lock picking in WotLK FWIW - have seen no chests, have found no lockboxes, and have not encountered any doors that couldn't be opened just by talking to someone near them...

I entertained the idea of engineering as well but after reviewing it decided against it - it really provides nothing essential - I hardly ever have to repair anymore - maybe after 5 instances and I have plenty of time to do that when I'm selling stuff in a city somewhere, and engineering really doesn't provide anything useful to make your character perform better.

Honestly for sheer performance as said before your best bet is BS/JC or if you're a tank you could use mining/JC (since the 500hp from mining is greatly useful for a tank and will make some good money).

JC also happens to be the best money making profession there is right now on top of being the best for character performance, especially for a fresh 80. My DK tank is in mostly epics and I'm still using 2 JC trinkets because they provide something like 110 stam each plus dodge, etc.