I have MySQL available in both development and production environments, so is it worth even considering SQLite3?

In a word, no. In my opinion, MySQL is better in practically every conceivable metric. The only thing SQLite has going for it is that it doesn't require you to have a database server installed and running!

My favorite use for SQLite is in tests for modules that use DBI. It's so much easier than requiring end users to give you host/user/pass to a running MySQL.

-sam