Status update: success so far!
My WiFi dongle had the 4.x firmware and of course could not hold a connection any longer than a baby can hold his ...
So, on the Uniden installation page, I skipped down to the Sentinel installation. Installed on top of the previous version, and the program would open just fine, but I could not "pin" the Windows 7 task bar button. Uninstalled and reinstalled, now I could "pin" the button.
Here, due to the cable layout in my home, I varied the procedure:
1. Turned off scanner, removed the 16GB SanDisk microSD card, and inserted in into my PC.
2. Ran Sentinel to "update" the firmware (actually, on the card).
3. Properly ejected the card from the PC and inserted it into the scanner.
4. Turned on the scanner (with the WiFi dongle already connected), and it immediately updated the scanner firmware and then (after a short delay) updated the WiFi dongle firmware. Note minor bug: while the screen remains lit during the scanner update, the background light is off during the dongle update.
5. Configured the WiFi dongle (WPA2 infrastructure), and then it successfully connected to my WiFi network.
6. Then I realized that I had configured my DHCP server to give the dongle a different IP address from the one I wanted it to have. So, I updated the DHCP configuration to specify the desired IP address, and thought I'd have to wait for the DHCP lease to the dongle to be renewed (1 hr), but in a couple minutes, the dongle picked up the new IP address, which I can ping. Based on prior history, this is a very promising sign!
Edit: It appears that the WiFi dongle is attempting to get a new IP address every 5 minutes or so, in CLEAR violation of the lease period that was issued to it (2 hrs). If that's the fix for the frequent disconnections, it is the WRONG FIX (namely, a bandaid). Furthermore, rather than doing a renewal request (like the other 20 or so devices on my network), it is requesting a new address each time (with a DHCPDISCOVER request). Of course, the DHCP server is just reissuing the same address, so everything appears to work. For now.
I have not tried the remote control software, but I will (hopefully, later today). I have little interest in monitoring the audio on my PC, so I don't intend to try that unless someone needs a test.