Tony,
If you are asking me if I think it is the belt... I'm going to have to lawyer up here: "Anything I say, that could be construed as advise regarding the wear, lack of wear, age, lack of age, or replacement of the drive belt on your 2002 SilverWing is only my opinion or an estimation of what I might do or might or might not have done."
The belt slap issue is annoying, but really only presents itself for very brief periods of time. It has a regularity and a repeatability to it. It is audible when you roll onto the throttle while at speed. I mean really roll onto the throttle. It is brief and I've not heard it byeond the acceleration phase.
If you are detecting an odor that smells vaguely like (really) hot brakes then you are possibly experiencing belt slippage. Belt slippage is almost always accompanied by a squeal at slow speed acceleration. This is correctable and I've done this procedure, but like all thngs there may be some unintended side effects.
Belt Slippage Cure(?): Place front tire solidly against a solid object that is not likely to move (tree, concrete block wall). Engage front brake, and roll the throttle hard, hold it for 5 to 10 seconds. You will smell a very offensive odor, but that should resolve the belt slip. You have however just super heated all of the clutch surfaces that come in contact with the belt and possibly the variator faces as well. It is possible that going into the belt case and cleaning all the surfaces and removing all of the dust would result in a similar outcome.
Belt Age: Again I've never heard of a belt failure due to age. If concerned about it - replace the belt.
If you are going to install the JCosta then you have options - perform a thorough cleaning - replace the belt - ?
Me, I'd ride that thing, it's just not that annoying to me.