I've posted before that I think superhero comics provide a good model for this - heroes like the X-Men or the Avengers are "strangers" in their own world, whose only real peers are the supervillains that they fight. Yet (at least in my case) when I'm reading the X-Men I don't ask myself "Why don't the X-Men just take over the world?".A problem with Points of Darkness is that once the players have gained a few levels by confronting darkness, it is often tempting for them to simply throw their weight around in the normal areas, where opposition is quite light compared to the dark areas.
<snip>
the PCs become strangers in their own world, governed by their own rules and gauged on a power level normal people cannot achieve.
It's not that the X-Men comics have an answer to this question; it's more that they present the whole situation in a way that presupposes that we're not worried about asking that question. I think D&D - at least, high level D&D - works better if framed in a similar sort of way, just taking it for granted that the PCs and their enemies belong to this strange, non-normal world, where the stakes are higher and the powers greater, and the PC team is not particularly interested in mundane things.
Even when I've GMed "evil" campaigns, the PCs' goals haven't been money and temporal power for its own sake. Their goals have been magical, cosmological power, which once again locates their concerns, activities, enemies etc in the "non-normal" part of the world. The everyday world is largely left behind, in play, except as a backdrop.