first for the objects you dont have something called worldPosition as you mentinoed in your expression..
it would be like this
vector $sphPos = <<sphere.tx, sphere.ty, sphere.tz>>;
if ($sphPos.y > locator1.translateY)
fluidEmitter.rate = 200;
else
fluidEmitter.rate = 0;
that is the correct way to write your expression dude. but for the rest i didn't get the idea yet of what you are trying to do.. sorry