I agree. Follow the directions and if possible use the whole tank up and re-fill with pure gasoline. I do not think letting the seafoam/gas mix sit for long periods of time in your bike is advisable.
In the fall of 2009 I purchased a 1980 CBX whose last tag was 2001. It would not idle but ran ok at higher rpm. I filled the tank with new gas and the recommended amount of seafoam then rode for about an hour. The bike sat for several hours then I rode it back another hour using up most of the tank of gas. About 30 minutes into the second hour I stopped at a redlight and the bike was idling pretty good. It continued to get better, and I have since run several tanks without SF and it is still running good, probably better with each tank. While this may not be typical, it was my experience and I am a believer.
I have to think that the PO properly stored the bike using Stabil or draining the bowls, because I don't think if it was really gunked up that it would have cleaned out so easily. Hopefully you will have a similar experience.
I will at some point pull the carbs to check float height, accelerator pump and choke settings, but for now I can ride.