If there was a Ziggy Stardust movie, or more realistically a Bowie biopic, I nominate David Brighton to play him.
He also sounds like him:
http://www.youtube.com/watch?v=ykAYYgnpmps
And here he is in an ad with Bowie:
http://www.youtube.com/watch?v=DxtoqnEpyLA&feature=related
Stephen Spratt could make a good older Bowie too:
^Real
LIE^
/obsession