I don't think there is a worthwhile substitue for the real thing.
And yes, they are endangered as they occur in the wild, but they are farmed like chickens. No worries of the domestic species dying out I believe.
So if you shop around, you can find capes with lots of splits pretty cheap - relatively speaking. Splits are no big deal, just put a spot of glue on it and pull it between your fingers. I wouldn't do that for a show quality streamer, but I don't tie those so it's not an issue for me.
The jungle cock is there to be the "eye" on the streamer. I've read many times that fish target the eye of their prey species when attacking. Personally I like to use it and always do, but Pete is right you don't really need it.
Do I think it helps me catch fish? Yes. Do I think it will make a difference in helping you catch fish? I can't really anaswer that - that is a question you really have to answer for yourself!
It means you have to fish more to find out tho... Sorry about that...