I have been following your discussion regarding Vault on the newsgroup and I think you have some very valid points. I can see why Autodesk felt it was necessary for a larger firm such as yours to have something beyond data shortcuts to allow multiple users to share data with Civil 3D, but I think they approached it from the wrong direction. Whether they want to hear it or not, keeping all of the objects and data within the model is a mistake, especially when the model itself has proved to be this unstable.
I have the luxury "?" of being the only person in our small office willing to even try Civil 3D so sharing of data is of no concern. Even so, I have been pulling everything I could from the model, keeping only the corridor and surface design there and reference other design elements back in from secondary design drawings. The drawing structure is more complicated, but my file sizes are quite small and I experience few crashes. Occasionally a data shortcut will break when the drawing becomes disassociated from the project but that is an easy fix.