Why not allow the user to decide wether he prefers the original iOS3 or the WD7 design? It'd be cool to see something like a theming tool inside the Settings app which gives one the ability to switch back and forth between themes. And I mean like manual theming not the Winterboard one. Or you could just release an unthemed but tweaked version of Whited00r and leave a zip file with images for manual theming. And disabling the WDUI substrate shouldn't lead to a SpringBoard crash 
A lot of the graphics in whited00r rely on the UI tweak doing behind the scenes work sadly
Otherwise it would be possible to just swap out the images like you say.
Grayd00r, the new project for iOS 5 devices we are building, does actually give more choice, or at least it is being designed to in the long run. Much more choice than whited00r actually
That system may be able to be back ported for some bits when it is completed and stable, to use in whited00r.
