Well worth it imo. lighter wheel/rotors/tire assembly will accellerate turn and stop more quickly.
lighter wheels are less rotating mass which allow you to in theory turn quicker.
in reality the odds of you feeling any difference is not realistic except in your mind.
If you're a hardcore racer and you feel this is essential to shaving time...then go for it.
01-04 wheels and rotors (rotors are same as busa basically)...front should bolt up no issue but backs have different spacers.
05+ will be a different story.
If you want to actually shave weight....go to a newer setup with the lighter wheel and smaller rotor...but then in theory the smaller rotor should stay hotter longer and allow brake fade quicker. Not bad on a lighter gixxer but maybe not a good idea on a heavy busa.
Before I went through this hassle, I would focus on my braking system and improve my choice in tires. 10mm raise to the rear and sliding the rear axle forward will make the bike feel more responsive than lighter wheels ever will.
If you want the bike to really feel "twitchy"....drop the front tire from a 70 series to a 60 series

lease:
My gixxer has a 60 on the front and it took some getting used to.
I have a set of busa, 03 1k and 07 1k wheels on hand if anyone wants weights? Sorry...no cush drives.