I know the shells on motorcycle helmets expire after 3-4 years. Most companies recommend immediate replacement after even the slightest crash. I guess you would have to ask yourself "how much is your head worth"?
Definitely. Had a friend who started park recently and only had an old ski helmet from his dad to use. The thing split in half on his third or fourth fall and the foam on the inside was forming into this weird powder-like material. I mean that helmet was probably more like 20 years old, but it never hurts to get a new one. They aren't terribly expensive.
ive got a Smith Maze and a Bern Watts that both have no impacts on them. I use a Bern Baker now and have no use for the others. PM me if youre interested and ill send you pics and a really good deal on them.
Never Summer Evo 153/Restricted ReFlex Cartel
Gnu Danny Kass 156 BTX