72nd Birthday, congratulations! I'm only 55 so I have a few years to catch up to you. And I can relate to the engineer mindset, we are a very technical breed.
Question time:
1) When you installed 9.10.2, was this an "upgrade" or was it a "clean install"?
If this was an upgrade then I'd create a configuration backup with the hopes that it may have some relevant data remaining but I'm not very hopeful. If this was a clean install then don't bother making a configuration backup.
Action time:
1) With the system powered off, disconnect your hard drives at either the SATA or power connectors. We don't want the drives being seen yet. I only do this as a precaution.
2) Perform a clean install, not upgrade, to the USB flash drive, ver 9.10.1-U4 (or whatever verion last worked). I would only use a single flash drive, not a mirror of two. I can explain why later but mirrored flash drives is something I don't agree with. Some extra things I like to do is if the USB Flash drive was previously used and could be considered suspect, I like to wipe the USB flash drive using my favorite tool (SDFormatter V4.0) and ensure the device is the proper size when done. There are many other tools that can also do the work like MiniTool Partition Wizard. Thsi step is not always needed but when troubleshooting FreeNAS with a USB Flash boot drive, well what can I say.
3) Boot up to FreeNAS 9.10.1 and all should be good. If it works then shutdown, plug in your drives and power back on.
4) Now cross your fingers and see if you can import your volume.
If you are able to restore your pool and data then I'd recommend you backup all your important data to DVD media or similar. I would then reconfigure your system settings and once all that is done, create a backup of your configuration file. Lastly I'd wait to see what is going on with 9.10.2. If another update comes out (I suspect it will), then wait 1 month to see what the fallout is.
If you are good using 9.10.1-xx then I'd just stick with it. Also one last bit of advice... When you do upgrade, if you get an alert stating to update/upgrade your pool, just disable the alarm and ignore it. Once you upgrade the pool features set then you cannot go backwards to an earlier version. The feature sets have never been important to the general home users in many years.
I hope this helps and feel free to ask any questions of me. I'm not the most knowledgeable person here but if I can't answer it, someone will jump in and offer up their two cents.