In the past, I have often created cells where most of the cell's geometry was set to NO SNAP, save for a few points (literally), that were intended to serve as key snap points. These SNAP POINTS were the only elements in the model having their snappable property set to TRUE. This was extremely helpful once the cell was placed in a model and I now needed to snap to a key point. I could now easily and confidently snap to the end of a fitting.

Placement points are similar by nature except that they are currently use for cell placement origin. I would suggest that placement points are perfectly suitable to double as snap points. This could be a selectable property when defining the placement point.