Not sure how applicable this is to your bracket, but from what we've seen in lvl 1 or 5 twinks is that leech does not scale well.
The amount of tertiary stats available is very scarce. So with the low percentage you will get of that tertiary stat, you are better off going for Speed. Even in low percentages, Speed gives you a very large advantage on the battlefield.
Of course if you are in the mind set that "some heals is better than none", it will be useful but I would suggest to use Lifesteal enchants.
Positioning in BGs is everything. Speed makes that easier.
I think once you get into BGs and upped to 29 it gets even worse... you could get leech on every piece if you farmed WoD dungeons long enough (dont think that changed for SL) but probably only get to maybe 8-10% at 20. Awful grind for it too.