multisite share

I have searched for several weeks now for an up-to-date tutorial on sharing event data. I am running multiple sites using Drupal 6. One of the sites has an event calendar that most of the others need to replicate while also being able to add their own events. I have successfully implemented sharing using the iCal view on the main site and the feeds module with the iCal parser on a client. Unfortunately, I can't get the iCal feed to include any additional fields. I need to have taxonomy information and a few other fields shared.

I'm about to decide whether to use a multisite approch or simply copy my drupal installation to another site and make some changes to it there. The problem is that both sites share 80% of their content, but not all. When I edit some of the shared content, I want it to appear on both sites.
So is there a way to share parts of the content between two sites in a multisite setup? Something like that I can configure for each page whether it should be available on both domains or only on one. I know I can have completely separate or completely identical content, but is a mix possible?