What's the lifespan of a poorly cooled Raspberry Pi? How do they hold up long term? Is there any advantage to cooling these things if you're not currently having problems with your setup thermal throttling?
And no, if you aren't experiencing throttling, then cooling them isn't giving you any advantages. Marginally prolonging the life of a $35 computer with a $5 fan isn't cost effective- consider that when you have to buy a new one in a few years you will be able to buy more performance for the money or get the same performance for much less. Think about the upgrade from the original Pi to the Pi3, or the cost drop to the Pi zero.
I've actually had more PC equipment fail on me (hardly surprising given their increased complexity) than Raspberry Pis, so they can be quite resilient little things.
It's solid state, there is nothing mechanical to break. I've had two running continuously since 2014. Use a ramdisk. No issues.
Mechanical failures do happen with solid state devices, even if they are operating within their specifications. Manufacturing defects (and gaps in testing), inadequate validation of all conditions within the spec, and/or inaccurate predictions of failure rates over time can all cause this.