I agree with you that wire at the thorax will make the fly "nose" heavy and sink like a jig. Another option is to tie the wire on the rear half of the shank and the the nymph will sink tail first. Either method is valid, just depends on how you want the fly to appear under water as it sinks.
Choices, and choices, and choices. I still have a lot to learn in tying flies, but some guys from the local TU chapter meet every Saturday morning, and I'm invited if I bring doughnuts. HA HA! But seriously, I have learned alot just in the last month, blows my mind.