Well, I'm not sure I figured it out, but I'm up and running, nonetheless.
To get around the problem, I decided to perform a full install on a PNY SSD that Best Buy had on sale today. I figured, if it was a problem with the USB interface, or pfSense's mounting/unmounting of the USB drive, then this would get around it.
I was wrong.
Here are all the different issues I saw in total, starting with trying to run NanoBSD.
When trying to run NanoBSD:
I couldn't get the BIOS to boot the USB when using:
Windows, extract with winRAR, burn with disk imager
Windows, extract with winRAR, burn with rufus
Windows, extract with 7zip, burn with disk imager
Windows, extract with 7zip, burn with rufus
I DID get the BIOS to boot the USB, using OSX, with the terminal command 'gzcat pfSense-blahblah-image-name.iso.gz | sudo dd of=/dev/rdisk3 bs=1m'. However, this is where I ran into the issues detailed in the original post.
Fast forward to this evening, when trying to run a full install:
Again, I couldn't get the BIOS to boot the USB with any of the combinations above, this time INCLUDING OSX. Frustration!!
I decided to go 'old school' and burn the ISO to a DVD. STILL wouldn't boot! At that point I determined it had to be something funky with the BIOS settings, because I noticed these devices weren't even showing up under the BOOT tab of the BIOS settings, like I'm used to seeing.
I started playing around with BIOS settings, I found, under the BOOT tab, a 'Compatibility Support Mode (CSM)' that was disabled. I enabled it, and I set all newly displayed options to "Legacy Only". Save settings and reboot into BIOS. EUREKA, the boot tab shows both the DVD drive and the USB drive as bootable devices! I proceeded with the USB drive, installed pfSense to my SSD, and now I'm up and running. Fingers crossed, I haven't seen any issues.
The reason I stated that I'm "not sure if I figured it out", is because after finding that BIOS setting, I never tried to run a NanoBSD setup to see if my original issues were gone. The only conclusion I can come to is:
1. BIOS settings were incorrect, causing it to not recognize boot devices, when that boot device was created with Windows/image writer or Windows/rufus.
2. Somehow OSX wrote the NanoBSD image to the USB drive in such a way that the BIOS recognized it, and booted, but pfSense didn't like it for some reason, causing the issues in the original post.
3. Once I changed the BIOS settings to recognize the boot devices, I can only assume that running NanoBSD using a USB drive written using rufus, etc. would have worked just fine, and I wouldn't have needed to buy the SSD in the first place.
As it is, I'm completely happy running a full install, and I hope that all the "pfSense killing SSD" gloom and doom posts are blown out of proportion considering today's hardware being vastly superior to legacy SSDs.
Sorry for the long-winded post, but if anyone else runs into these issues, I wanted to document my experience, and how I got going, before the information falls out of my brain (ie, tomorrow).