About the aerodynamic advantage, as I said, it's anecdotal evidence. But nobody has proven the opposite, either, that fenders slow you down.
I am unconvinced that their absence in the pro peloton is proof that fenders don't offer an advantage: In 1929, few pros used derailleurs, even in races that allowed them, but does that mean they didn't offer an advantage? In 1988, none of the pros used aero bars. Once again, if they offered an advantage, pros would use them, wouldn't they? In both cases, the technology had been established already (among the cyclotourists for derailleurs, among triathletes for the aero bars).
What we forget about racing sometimes is that as long as everybody is on the same technology, it's a fair game. And the recent UCI rules specifically attempt to outlaw any technological advantages. It's supposed to be a race between men, not between machines. For the latter (a competition between machines), the French organized the famous technical trials.
(No commercial plug here - I have bored most of you already by pointing out that the latest issue of Vintage Bicycle Quarterly chronicles the technical trials...)
Jan Heine, Seattle