Mac mini is accessable by ssh, but won't show up in finder

I have a mac mini running 10.6.8 that I use primarily as a web server. It is connected to an AIrport Extreme (2nd Generation) via both Ethernet and WiFi.

I have never had a problem accessing the machine via ssh. And usually find it in the Finder on my iMac, and can then access it via Screen Sharing with no problem.

However, I frequently discover that it is no longer visible to the finder, even though I can access it via ssh, and it is serving up web pages with no issues.

1- Can someone explain what is happening?

2- Is there some way via ssh access (I have sudo access) to "wake-up" (or whatever term) the mechanism (whatever it is) which allows the finder on the iMac to see the MacMini, and initiate Screen Sharing.

3- YES, the AirPort Extreme FREQUENTLY (i.e. daily on what seems to be about a 28 hour cycle) "craps out" on the Wi-FI side of its service. The Ethernet ports stay active and pass data, only the Wi-FI portion dies... it them seems to "self heal" after about 1-2 hours. This particular issue is a whole different problem, but may impact on the access issue. (And I have several ways in which I have verified what is happening to the AE, but no fixes yet... and naturally, it's out of warranty, so Apple's answer is "buy a new one.)