In summary, if you like getting into uni quickly and relatively easy, HSC is important.
It's more important if you feel you're going to struggle to meet what you want, because back paths are never really easy and take more time.
It's more important if your aim is getting into uni.
It's less important if you are pretty confident of getting into what you want and that's all you want.
It's less important if you are just doing the HSC for the HSC certificate.
HSC is important when you want to get into uni; its just that once you get into what you want it's irrelevant. Listening to those people who barely try and got into what they want, then trash the idea of HSC may not be such a good idea if you're currently set on a path you don't want to go down.