I am also currently struggling with the development of a strategy of using a single pln file for the attributes to link it to multiple files of a single project. As you said it, big projects are becoming a big problem in handling them on our daily work.
The attribute manager from AC is cool in a way that it shows you all the attributes in the project and which are in use. The biggest challenge is to synchronize these attributes between different files. You cannot use stories but go through the attribute manager!
Creating a new attribute (ex. Composite material) in the attribute.pln is easy, as you can simple append by index in the other files. It starts to get tough when you delete attributes. In this case you need to have a clear overview of which attributes have to be deleted in the other project files, and of course it must be done manually!
It would be much easier to have an intelligent attribute manager, either integrated in AC or stand alone, which would compare status of the attributes between the attribute.pln and other files and mark then in a logical way for the user to take necessary action.
Currently I see it as a painstaking management to synchronize manually all the attributes, and if you by mistake delete or overwrite a valid attribute, good luck in repairing the mistake.
I am working on this strategy for some time now, and if I get any lucky with a useful and efficient way, I will keep you informed…
The BIMster @ AllesWirdGut
Currently: Archicad 26
User since Archicad 6.5 (2001)