The main reason LDView's icons are so simple is because I drew most of them myself, and I definitely don't consider myself to be artistic. And you're right, if you use a third-party set, it becomes really difficult to match the style.
Also, if you want to support standard toolbars in Windows prior to Vista, all the toolbar icons have to use on/off transparency, instead of multiple levels of blended transparency like the LED icon set uses. This of course wouldn't be a problem for you, since all your UI is done in OpenGL. (At least, I assume it's all done in OpenGL.)
I do find that having the icons helps a lot, and having them be colorful also helps a lot. I'm really disappointed in Apple's recent decision to make their toolbar icons monochrome; that really cuts down on their utility, since you get used to aiming based on color, and that's just not possible with monochrom icons.
Also, if you want to support standard toolbars in Windows prior to Vista, all the toolbar icons have to use on/off transparency, instead of multiple levels of blended transparency like the LED icon set uses. This of course wouldn't be a problem for you, since all your UI is done in OpenGL. (At least, I assume it's all done in OpenGL.)
I do find that having the icons helps a lot, and having them be colorful also helps a lot. I'm really disappointed in Apple's recent decision to make their toolbar icons monochrome; that really cuts down on their utility, since you get used to aiming based on color, and that's just not possible with monochrom icons.