What I mean, is to have the menu, toolbar, and dialog icons in SC all reference portions of an external "buttons.png" image. That way users could create and contribute different icon sets. I think there is a lot of room for improvement (visually speaking). For example different images for the different types of "Grabs" on the Capture menu, or the different types of Borders on the main toolbar.
Given the high number of items, I imagine you'd want more than one group of images. Maybe "MeniItemImages.png," "ToolbarItemImages.png," and "DialogItemImages.png." The dimensions of the pngs would be 16 pix high* (16* number of items) wide. Here is an image of my work space for the skin I made for xplorer2 http://i.imgur.com/aCC4F.png
If this is something you're interested in, I'll volunteer to put your current images into groups. Those groups would be part of the download package for SC, and then folks can create custom versions at their leisure.