Valvetech is just an additives package that is added to the fuel after delivery to the marina. I have been using it for a couple years now since that is what the fuel at my marina is and I can fuel in-slip (plus they have a good cash price). I have no empirical evidence what difference it makes, seems like the Racors last a bit longer, or perhaps I have just got lazier about changing them while they are still in the yellow zone. We don't put near as many hours iin as in the past either. The engines run very clean, no soot on the transom, etc.
I believe the key is to get fresh clean fuel at high turnover docks frequented by commercial craft, better yet if they had a recent delivery but when in transit that's luck of the draw. Ocean Petroleum in Brunswick, GA used to stop selling when there was 250 gallons at the bottom of their tank. They get almost daily deliveries. My current dock qualifies on that score too. I used to manage fuel by strategically loading up at various places that met this criteria up and down the east coast, buying right off the truck where possible. My engine manual only recommends a biocide additive if the boat is to be laid up for awhile, and is at best neutral on others.