I'm now trying Joomla since it was next on my "to try" list and seems good also in practice, not only in theory. It has lots of nice plugins available too, which is nice. As I said earlier, I will also set up a separate Trac page as a development wiki for Spineless. I will keep you updated.
UPDATE: Switched from Joomla to Drupal now, thanks to ukdm for the suggestion! Feels much easier to work with than Joomla. :)