You're most welcome! :^)
Yes, you should be able to transfer the keychain to another Mac OS X machine.
The main problem with not having a re-importable copy of the certificate is that, should your keychain be corrupted or damaged (it unfortunately happens), you would have no way to get they keys back out into a workable setup. Should you only use your keys to sign your mail, this is of no real importance but should you use them to also encrypt mail, this means that you may never be able to decrypt these messages again. Of course, it is an unlikely situation but I have seen it happening (for reasons way beyond the control of the Keychain development team) and it could be an issue depending on the type of mails you exchange.