For me, I think there will always be more to collect. When I finally finish my Archie comic book collection (estimating 2-3 years from now), I'm sure I will start on another area. Also, since I collect original Archie art and other comic strip art, I will never truly be finished. And of course, there's all the Archie upgrades I need...
Jon's collection just staggers the mind. I suspect he's one of the very few generalist collectors that could be close to "satisfied" with the breadth and quality of his collection. I mean, I've owned Larsons and I've owned Churchs, but I've never owned both pedigrees of a single book