I don't think there is any problem with your locations - I've found wreckage off STV, the Wetlands, Tanaris, Azshara, and just about everyplace else I've found fish spawns. The problem is the wreckage is a rarer spawn - the best bet seems to be running up and down the coast fishing every spawn you see and watching for them to repop. Sometimes they'll repop as wreckage or debris.
Kind of like trying to find silver by mining tin, or gold by mining iron.