So far everything I've seen suggests that the only thing worth the $$ is better filtration.  If you can filter oil down to about 2 microns, you eliminate almost all wear from an internal combustion engine.  Most commercial high hour/high mile expectancy equipment runs 2 micron or less filters with some pretty impressive results.  A standard full-flow filter usually only gets down to 15-40 microns depending on the filter/application.  I would guess (based on casual observation, nothing scientific) that our Savage filters (emgo or factory) are closer to the 25-40 micron range.

I agree that most additives are snake oil. I did have excellent results with Techron once on a Honda Prelude that sat for 2 yrs with old gas in it. IT made an amazing difference in two tankfuls.  We're talking about a car that stalled at every light if it wasn't revved to 3500 rpm. I went thru 3 tanks of fresh gas with no luck , until someone suggested Techron. Improved by the end of the first tank, and purring like a kitten by the second tank. Not exactly double blind testing but I was very happy to avoid a $800 quote for replacing the fuel injection system and the only thing changed was the Techron.

No experience with Seafoam in a bike but know lots of happy people with Mercury I/O's that swear by it.