From what I have been told by some people is that it depends on your degree.
I was told that Law, and probably business degrees (I know nothing about those) and various others it matters a fair lot but for Arts (what I am doing) it matters less on your Uni and more on your majors, how you understand them and how capable you are at applying them.
Also, it depends on what kind of work you want to get into. Although, a higher regarded university generally means that your degree will be regarded more highly.
Not everyone gets into Sydney, but its often best to make the best decision you can with what you have. Although make a decision you can live with, go somewhere you want to go with classes you like, and if you go to a not as good uni because it has a course there that you want to do more than another at a better university do that.
It can be important but its not the be all and end all.