I also heard a theory, I think it was at Whedonesque, saying it might have something to do with the "Shanshu prophecy". Sans in French means without, so sans shoe - without shoes. Therefore when spike is "drowning in footwear" he's is with shoes in a big way, and - according to the theory - the vampire the Shanshu prophecy was meant for.
i read somewhere that, can't remember where, but someone thought it was somwthing to do with The Shanshu as well...in S5 of Angel, Spike calls the prophecy 'Sans Shoes' which i suppose lends itself to N4H's theory.
I read once, but I can't swear to it, because I don't speak French, that the word "shanshu" is simply the French word for "vampire," Maybe some of our French speaking readers could affirm or deny that...