Yes, but we were limited by MySQL each time. Have you used Postgres or Oracle or Sybase before? I have a hard time expressing briefly how great SQL92 compliance is compared to the subset that MySQL supports. Using MySQL for this is walking the long way around the bay when you could paddle the Postgres canoe directly across it in a fraction of the time.
From a Project Management standpoint, I'd be very interested in knowing
what's stopping us from breaking this into two projects.
The first being a redesign of the table space, and upgrade of the DB to the most recent version of Postgres, with modification of the current PHP code. This could be an evolutionary process, with the one "revolutionary" moment being the upgrade to Postgres and concurrent update of the PHP code to remove the MySQLisms. Once we are on the new system, the tables and queries could be updated a few at a time to improve performance incrementally and evolutionarily.
The second stage would then be upgrading -- with the improved table structure -- to the new ModWiki software.