realistically, its the ranks that matter. When they say moderated, they use the ranks and the gaps between people (plus a few statistics things, it's a bit grey) to scale the set of hsc marks for a given school in a given subject. Thus, coming first in a subject after all internal marks are counted is a very good thing, because you automatically get the score of the top mark for your internal 50% of your HSC subject mark (your external 50% is based on the mark you get in the HSC exam and a difficulty scaling which is recalculated each year).
You should probably look this up in the specific part of the forum because it's beginning to get messy in my head and that isn't doing good things for clarity. Suffice to say, good ranks are good, with consideration that the gaps between you and the people above you aren't too big.
With regards to the estimate - its better to have a good one because you have a better chance of getting a 1st round interview, but not critical because there is a 2nd round of interviews for people whose real UAIs were sufficiently higher than their pediction. The predictions aren't used for calculating admissions though, if that's what you're wondering.
What trev said is an annoying situation, but the chances are if someone needs their estimate lifted significantly, they may not have got a good enough UMAT to start with and won't get an interview anyway.