I expect that completely ignoring your quirky interests leads to completely destroying your motivation for doing useful work. On the other hand, I find myself demotivated, even from my quirky interests, when I haven't done "useful" things recently. I constantly question "why am I doing what I'm doing?" and feel pretty awful, and completely destroy my motivation for doing anything at all.

But! Picking from "fiddle with shiny things" and "increase global utility" is not a binary decision. The trick is to find a workable compromise between the ethics you endorse and the interests you're drawn to, so that you don't exhaust yourself on either, and gain "energy" from both. Without some sort of deep personal modification, very few people can usefully work 12 hours a day, 7 days a week, at any one task. You can, though, spend about four hours a day on each of three different projects, so long as they're sufficiently varied, and they provide an appropriate mixture of short-term and long-term goals, near and far goals, personal time and social time, and seriousness and fun.