Stew,
like you, I've been a longtime (god, 20 years now!) proponant of the West System, but a recent series of projects has convinced me to jump ship. I now use System Three products.
the primary advantage of S3 is that it's FAR less finicky about temperature, humidity, mix ratio accuracy, etc. It's much more friendly and reliable for us backyard-workshop types. Let the pros with their climate-controlled shops use the West.
of course, your local marine store probably doesn't stock system three on the shelves. Jamestown Dist. carries it, but because they ship for free I generally order direct from the factory. they have a website and an 800-number.