Sciences in the HSC:
Are not:
Compulsory. Only 2 units of English is compulsory.
Elitist. Anyone can do them.
Harder than other subjects. There can be some abstract concepts and a bit of theory to remember, but they're not incredibly difficult with some work.
Something you should do just for "scaling". Instead do them if you like science.
Are:
Fun
Great prior knowledge for a lot of uni courses. Chemistry, physics and maths will help you a lot through first year of any type of science or engineering degree.
Worth doing - you can also "drop" to Senior Science if you find it hard in year 11. The specialised courses are a lot more rewarding though.