... Mark, honestly, you do not need to understand how vcaa allocates marks. Just do the best you can in each subject.... that is all that matters. Besides working hard to hopefully do as well as you can, marking (of VCAA exams and the determining of the final ATAR score) is out of your control and of course out of everyone here's control as well... unless someone so happens to be part of VCAA?!
Just make sure you do all the pre reqs required for med. If you really wanted to play around with the vce scaling system i.e. wanted an extra boost in your ATAR score... do a language (
guaranteed scaling of at least five I believe? Did the Government intervene regarding scaling for languages? Or was that just a rumour...? Please correct me if I'm wrong) rather than a subject that scales down even though the subjects are widely perceived as 'easy.' As Russ said, 'there is no such thing' as an 'easy 50 subject.' Another thing to add, languages are definitely not easy but will scale heaps if you are decent and put effort into it which will ultimately give your ATAR score a huge boost.
Anyway, at this stage, are you really sure you want to do med? You still have more than two years of high school to go, anything can change within that time as cliche as that may sound. Why not keep economics? Personally, I think econ is a very worthwhile subject to study.
... At the end of the day, pre reqs and choosing subjects that you're good at is the way to go.
EDIT: Regarding med, are you aware that entry into med is not solely based on your ATAR score?