How long do tweeters last?

I have a pair of AR-14's that are about 30 years old. I've replaced the woofers (reconed once, then replaced) but have the original tweeters. I'll also be replacing the caps in the cross-overs. The tweeters sound OK, but I can't remember what they sounded like new and my acoustic environment is different anyway. What do aging tweeters sound like? How can you tell they are no longer at their prime? Do they wear out? Thanks in advance for your help.
They shouldn't wear out. They just may not sound as good as newer models.