OTOH I suspect that being conscious of impermanence plays a role in why I am in something like a constant state of light depression. It is sort of hard to get really enthusiastic over things when you know you will lose everything you cherish one way or another with very high probability.

In something of a similar state. The other issue I struggle with is that I rolled a really high score for equanimity - coincidentally another Buddhist value, along with a consciousness of impermanence - and I've long wondered what role that plays as well. Descriptions of Buddhist enlightenment sound more like deep clinical depression than not to me, but it's possible there's information that isn't being conveyed.