To be fair, you shouldn't even run MySQL on an f1-micro. This is more on par with an 18 vcpu raw server, before you'd even consider any value that the software provides.

I'd certainly love to see us get to a world where we can split up a single spanner "install" in an isolated, multitenant manner, but even for a small company, $8k/year is admittedly a small fraction of one engineer. At a company with several, you can share your single Spanner instance just like you would any other database.

Disclosure: I work on Google Cloud (but not Spanner).