A few questions for you :)

[Falcon 269]

I would not worry about the cracked in let pipes, I am sure Mike will confirm that the rubber is just a covering over metal.
When I meet Mike at a Ivanising session he had a old set that he cut in half just to check.

There is a section of the stub which is solely rubber but as others have said, it's pretty thick.  I've never seen one crack all the way through but I did find some this year which had started to disintegrate and crumble.  They were from the same bike and it's not something I've seen previously.