An encyclopedia of weirdness

Well, I don't see it like that at all. There are not many SPN episodes that were true stand-alones. Almost every episode either moved the mytharc along or the development of the characters. What people call stand-alones are usually necessary episodes that deepen the characterisation and move Sam and Dean forward, either individually or as brothers, and while they may have monster-of-the-week plots that are finished at the end of the episode, they tell a continuous story about the characters. Just look at S1, for example - the season a lot of people consider to have almost no arc and a mostly stand-alone structure. Sam and Dean go from estranged to tentative reconnection to working through old resentments to understanding each other's perspectives to establishing a new, improved bond. All that happens in little steps throughout the so-called stand-alones, in a consistent and continuous development - and that's true for every season, so I can never see SPN as a true stand-alone format. :)