We had a Q&A in the TDN recently with the very prominent Dr. Wayne McIlwraith--he said there's some science to back up the significant positive effect of nasal strips:
http://www.thoroughbreddailynews.com...ent.cfm?id=507
One study he cited said "Horses with the nasal strip had a win percentage of 3.4% higher than horses that did not wear one."