Ghetto, if you know what substrate you are painting over its one thing, but with 30+ yr old bikes its often a toss up. I paint Peterbilts for a living so stripping down a motorcycle tank is about as inconvenient as a fiery sneeze for me, but really, there aint much to it. For a rattle can job, one might want the extra protection of the existing paint. But if yer gonna do it right then why not start with a clean slate? Painting over an old finish isnt "poor surface prep" but its not the best way to go about it either......Especially when an hour's time and a couple pair of disposable gloves will get you there......
Craig