this past January, it's been running since then. [...] But I agree about your suggestion in replacing the SD card with something more robust.

Consider making some changes: Log only to RAM (i.e. mount a tmpfs for /var/log and some other places), keep the SD-Card mounted read-only, or - if you have the memory - put everything you need into an initramfs and don't mount the SD-Card at all. If you want to keep the logs, copy them once per day or at shutdown to the SD-Card. Logging to another system (e.g. using rsyslog) could also be an option. Also, just using the noatime or relatime mount options (see Re^4: Analyzing Files Within a Directory) could help a little bit.

Alexander