I recommend everyone to do pretty much every trial exam they get their hands on (not sure if it'd be worth doing pre-2004 company exams, but definitely worth doing pre-2004 VCAA exams).
Really? I don't see the point doing ~60 if you aren't improving and/or felt you have done enough.
Probably should have worded better: I was really just talking about doing as many different companies as possible. Trial exams are to expose you to exam style, right? Different companies would have different questioning styles etc. I notice that once you do a few exams from one company, (a lot of the time) their exams stay with the same style, same difficulty etc.
For example, it wouldn't be as useful as doing like 8 Neap exams and neglecting the others. And of course, VCAA should take priority over any other exam.
But yeah, you're right that there's probably not much point doing 60 (or perhaps even more than 20 for matter).