Aki
I think the "spring" is to help the hose keep its shape. And no, it doesn't extend to the end. I am so cheap/stupid I usually blow a hose before I accept the fact that it is bad, so I am not the best at telling you how to tell if it needs replaced. But if you squeze it and it feels like it is fragile, or you know/suspect it has a lot of time/miles on it, they ARE CHEAP at any autparts store.
Rock