Staggered 18s were a factory option on the MSports. As were square 18s and staggered 19s.
Not sure the 19s help resale with that ride quality...they're not exactly in demand.
18" 355's, stock staggered:
http://e84.xbimmers.com/forums/showthread.php?t=892796
Plenty of us running aftermarket staggered 18s as well.