very interesting question, I do similar work. Actual the maps and number of tabs are not so many that I had the need to split.
I thought about how I would solve your issue.
Typically you have different phases in a project, e.g. design, implementation, testing, deployment, etc. I would try to organise the "master" map by this phases and hold in the "master" general information on the project. So for each phase I would generate an separate file in which I can organise the meetings in tabs. The overall number of tabs in each map is hopefully reduced and can be tracked. The pity is that links to other maps cannot point to an individual tab in the file.
Substructures for the meeting maps could also be build by audience, e.g. SteerCo Meeting, Customer, meetings, internal status meetings, etc. In the first map of such sub-maps I would generate one tab with an overview map, which give a short info on each meeting and a link to the detail tab.
PS: Patrick, I think this is a topic of general interest, maybe you can move it to the General section.