Anyway, the icy wind blasting through the window now is doing much to revitalize me, and I'm continuing to pursue the MultiPropertyGrid. Types that support String in their TypeConverter are editable via a simple text box, while enums are handled with a combo box. User entered strings are validated through the type converter to make sure they're valid, and if they fail the user is notified with a message box and the control's error template is activated. Flags enums might be a little more complicated. Maybe a multi-select listbox. Beyond that, types will need to supply their own WPFTypeEditorBase derived editor control through the Editor attribute. The type is then retrieved through the TypeDescriptor interface and instantiated and data-bound into the property grid.
Once this is out of the way I'll need to handle an undo-redo stack somehow, then maybe I'll finally be able to focus on the level format. At this point it's abundantly clear that there's no way I'll be ready in time for DBP 09, but it's still a useful deadline to keep motivation up.