Thanks to everyone for their responses. I went ahead and submitted a bug, but some good points were brought up about why insensitive is not complete. A user might not realize that they need to use the xml editor to select their insensitive item. It would still be nice if shift-click wouldn't select insensitive items, but maybe it is not the most important thing right now...
The sensitive/insensitive property of objects is not actively supported at the moment, because we plan to implement layers instead (a layer can be made invisible and/or insensitive) and then perhaps eliminate the per-object sensitivity.
I have been looking forward to the layers dialog, but I think it would be a mistake to eliminate per-object properties like sensitivity and opacity. I know that when I've done work in Illustrator I'm constantly using the layers dialog to flip the visibility/sensitivity of not only layers, but also individual items. In fact, I think that the Illustrator layers dialog may be a good model in general for the Inkscape layer dialog.
-Michael http://www.planet-zero.net