i think the whole premise of Archicad is "simplicity" - ie easy to use (though I do admit the whole interface still needs some simplifying). I think this level of customisation just confuses people. I think the way GS have gone with customisation in AC9 is however a good direction.
I agree with the idea of being able to change the size of the palettes. I'm not so sure about the color option.
Monitors are now being run at such high resolutions that the old 72dpi standard looks pretty course, and the icons can get awfully small. Given the variations in people's visual acuity (and the changes that come with age) it does seem desirable to allow users to set the size that works best for them.
Unfortunately, I think that this is probably quite difficult to do. In the old programming model this would require multiple copies of all the interface elements, which is a HUGE task. On the Mac side the Quartz engine probably makes scaleable interface elements rather easy, but, as far as I know, this cannot be done readily in Windows XP (and probably won't make it into the reduced feature set of Longhorn either).