My inspiration is almost always my own needs, I usually make things to scratch my own itch and put them out there hoping that others might have the same itch :)
I highly value human readable code, so I don't really use any of those, as I don't like the result. Of course over time I have developed a few strategies to keep my code DRY and maintainable, but I don't think what I do fits in any of these schemes.
I polyfill when necessary, and I ADORE polyfill.io because it takes all the hassle and extra weight away from polyfilling. For FOSS projects though, I think supporting the two latest versions of every browser (and no IE, just the latest Edge) is perfectly sufficient. Developers don't typically use older browsers. Any complaint I had about the websites of my open source libs not working on older browsers was from developers testing them there for the sake of it, not because they actually used that browser. So these days I reply to those complaints with "Thanks for the report, is this the browser you actually use?", to which they tend to back off and admit it isn't.
There are still inconsistencies and browser bugs, but the situation doesn't compare to when I started in 2005 (and think that that was the tail end of what we know as the browser wars!). These days, if there's a difference between browsers, it's either because one of them implements something and the other one doesn't, or because you hit some obscure edge case (I hit many of those, but I think I'm an exception there). When I started, ANYTHING you did on the Web, you hit browser bugs. A good developer back then wasn't one with good knowledge of the specs, it was one with good memory of all the browser bugs. We're way past that now.
I imagine how awesome it will be once I finish what I'm working on and people can actually use it, what they will make with it etc.
I go to a nice restaurant (see my answer to Juanita above) :)