Great Question!
I used to use VP fuel all the time on my earlier bikes but have not tried anything out on the 99. I recall a very long thread here about fuel and the components of it all. If someone can find that pls bring it back up?
I would do a trial by diluting it w pump gas and see how it runs. Then do a full tank and calculate the mileage by hand to see if it does anything there. Unless you dyno it there is no real way to tell, unless you are that good you can feel a difference. I am waiting until some cooler weather before my dyno runs. This east coast hot humid BS will kill your numbers!