It's finally gone!!!
The main tools toolbar has been forced into a stock GtkToolbar. Now that it is no longer a limiting factor, Inkscape is much more usable on screens 1024x768 or smaller. Any tools that don't show up in what space the toolbar does get just end up under the popup menu at the bottom.
On the setup I'd been checking size on previously this now shrinks the minimum size down to 535x469 (and on my Eee PC that hight is down to 460... very usable there).
Also in all the cleanup I was able to get in some needed fixes to floating out the toolbars.
Previously I'd whittled things down from 652x735 to 600x583. So it's over 36% shorter than before.
Overlaying this new size on top of the previous comparison really shows the difference.
I avoided some of the work of changing legacy code over by wrapping things in a simple Gtk::Action subclass (yay C++) so was able to get things functional much sooner than I'd hoped. Now it's time to add a few more things... especially since the cleanup I did manage to do put things in place to have string-based UI.