It doesn't really pay to monitor a SOA, unless you have a high gain antenna or you are closer enough to monitor any since it's short range transmissions. Usually on scene communications where either they don't have good in building coverage from the system or don't want to tie up the system. Portables only put out about 3-4 watts mobiles 35. The SOAs are not used in base radios.
I think the first time i ever even used a SOA channel (in the 8 years that i have been using ARMER) was when Nate put it on the ICS205 for the Lake City Funeral.
My suspicion is that the most common user of the SOA's is the BCA, but they have action pending with the SRB to encrypt their activity on those frequencies. Maybe there is much more activity on the SOA's with LE than i know about, but generally speaking, most end users really don't have a great concept of how the system even works aside from when they PTT, it works.
In the metro, we have 13 SOA resources, 6 are Project25, 7 are analog and 2 of the analog resources have a repeater.
And honestly, If an agency doesn't have 10 times as many resources on ARMER as they will ever need, then their System Techs are not meeting the unwritten standard.