This was my thinking and experience when I set out to build Cachoid[0]. There's so much to gain from caching stuff in RAM it should be ubiquitous. The thing is CDNs don't always have the scale to stick all tenants in RAM. Hence the caching to disk.
> Do we really need three expensive dynos, or a $50/mo database plan?
Sounds like there's the chance to optimize for what is, as they say, a static website. Why for a database that you're not using? (And what kind of a database plan do you have when it costs $50/month when it's apparently a (nearly?) empty database?!)