Key metrics for assessing network health and performance?

What statistics do you look at on your OpenWRT routers as key metrics for assessing the health and performance of your network? What types of things might be red flags that problems are happening or will happen soon? I realize this is a fairly broad question and I intend it to be so. I'd just like to hear what folks out there are doing.

Network health and performance? No box that I'm running OpenWRT on has even remotely enough power to run an IDS.

Router health and performance:

  • uptime
  • remaining space on /overlay/
  • occasionally glancing at errored frames on the Ethernet interfaces
  • occasionally glancing at the logs (I split wireless logging that is below WARNING from the rest, so the remaining logs are actually readable)

Basically, at least as I deploy OpenWRT, there isn't much to go wrong as they don't do much more than route packets.