If you are choosing to drop a subject because you don't like it, that's a good idea. If you're replacing it with a subject because it will be good for scaling, that's a bad idea.
I chose Japanese purely for its scaling, then did so poorly in it that it didn't make it into my primary four anyway (and so its scaling was basically useless).
Looking at your subjects/ATAR reqs, I'm assuming you're wanting to do science at Melbourne (could be so wrong, it would be nice if you could tell us what course you want, as Reus has asked), but the fact that you have chem and methods basically means you've made a good decision. If you want to do anything that drifts towards science, as long as you've got those two, you've set yourself up well.
At the end of the day, as long as you take subjects because you enjoy them or think they're interesting, and not only because they scale well, you've made a good decision.