Fascinating spreadsheet - I only saw it after I tried to figure out some related formulae using the wowhead weights.
Your work on threat may benefit from incorporating some of the results of PsiVen on tps under different weapons in 3.0. I think it implies that some threat stats are better than others (notably strength>spell power) whereas you are implying they are equal. Here's what I think the data imply:
http://www.failsafedesign.com/maintankadin/viewtopic.php?t=12786&start=414
The more subjective questions are how to trade off effective health with avoidance with threat. But I will have to think more about that.
EDIT: The formula used for tankpoints sounds about the best simple way to combine avoidance and effective health.
http://wow.curse.com/downloads/wow-addons/details/tank-points.aspx?CommentPage=3#w_tankpoints
That is to say:
tanking health = H/(1-A)(1-DR)
where H = health, A = avoidance, DR= damage resistance
How to weight tps vs tanking health is trickier.