Some of us just really like digging through raw Martian Elevation data and turning it into models or textures or whatever. And learning a new language while we’re at it is a nice (intended) side effect.

If we could just “learn the language” cold we would. By all means, if you have something “useful” you need to do, prefer that. But we don’t always have that on hand, and fun toys are a good substitute.

Do you run filters to "sanity check" for continuity breaks, data noise bursts, etc, and setup for feature detection, relief highlighting?

Most of the things I've worked on in my professional career have been ultimately useless :(

Ultimately everything humans build will be useless. Haven't you gotten paid for them? That's what makes them useful for you.

Is it useless if it has value to the creator?