And while on the subject as someone else decided to start it off again.
As for the airbox mod on a Ducati if you study the text and graphs here
http://moto-one.com.au/performance/750ssie.html it can be seen that not only does it improve throttle response but it also adds approximately 5% more power from the middle of the rev range up to the redline which when combined with open pipes and the correct fueling curve gives a good 5bhp over the standard bike.
It is a cheap mod that has benifits something that most racers try to find and if it costs next to nothing, Yet it narrows the bhp gap on the competition its not suprising that racers would want it.
I would expect my 750SS when finished and set up with the airbox lid fitted to put out around 62bhp with the airbox lid standard and With a modified lid I could be looking at 65bhp.
Now with a class limit of 72bhp that some bikes will no doubt be very close to it doesn't take a Genius to work out that 72bhp - 65bhp = 7bhp difference which is better than 72bhp - 62bhp = 10bhp difference.