The 16 bit thing is irrelevant. Since people are still using these things, it can't be much of a problem.
If you are singing live through a PA system, the nuances of a piece of vintage gear will be lost, and the audience doesn't care. Also, moving the pcm70 from venue to venue will subject it to the possibility that it will get broken or stolen.
I understand getting the pcm70 for studio applications, but it is a complete waste in a live setting.