I guess it is time to shake this boat a bit.
I reuse my SD cards but I also use them as another layer of image backup.
One of my backup drives is a solid state drive, identical technology to your SD card, so I see no reason not to do it. I watch for sales on large capacity SD cards and then transfer image files to them off my computer.
Seems to work well. I haven't had a single failure nor have any of my cards admitted to engaging in questionable bad sector activity while sitting together in the dark. In addition, it is just one more layer of backup and they are certainly easy to store!
To my understanding almost all, if not all, backup systems are subject to failure over time. Of course this was known a very long time ago as "nothing lasts forever, not even a pyramid." So you may have to move your backup information to another, newer technology in ten or twenty years.
The biggest problem is labeling the little buggers in such a way that you know what files are on them a few years from now.
The reality is that nobody will likely care what is on those little cards when I have passed this mortal coil. And...if someone does, my memory is disappearing quick so they better start asking pretty soon.