Strength is useless for tankadins.  All our aggro is from spell dmg and the higher spell dmg bonus one has, the higher threat per spell hit you get depending on the spell coefficients for the spell.
Strength only gives 1 block value per 20.  Refer to the equation  [(Shield block value) + ((Strength / 20) - 1)] at http://www.wowwiki.com/Formulas:Block That's very negligible.  The equip stat that says "Equip: Increases the block value of your shield by x" is the way to get block value.  Strength is warrior's stat for aggro. Tankadin equivalent is the combination of equip block value and spell dmg.
In ohter words, if you want block value , get the equip stat "Equip: Increases the block value of your shield by x" and it will cost less in terms of item value.  If you want more aggro, get +spell dmg.