Here are some random thoughts:
It would be interesting or maybe helpful if the ampr.org name server did some statistics collection. These stats could be used to help prune dead records? I am not sure how resource intensive that might be however. It looks like you can use Cacti in conjunction with BIND.
It is also important that we have some idea what is on the amprnet, what it used for. The Michigan Digital Radio group has some basic activity polling : http://server1.nuge.com/~drg/network.html
Perhaps even something that can be installed on gateways that promiscuously monitors well know ports/services, and can be configured to report activity to a central page? If nothing else can the gateway portion of the portal have some additional text boxes, so folks can explain things a bit more like the old resource.txt?