You're right that many demos simply exist to showcase technical brilliance, but many in the demoscene are starting to trend further towards expressing artistic ability. Some examples off the top of my head:
I have a super-beta build working, if you'd like to try it out/help bugfix shoot me an email at "copodt at the google email" and I'll send it to you :)
"Lifeforce" was fantastic and really stand out from any other demo, event to this day.
"For your love" use the same kind of particles extravaganza that Fairlight popularized, but really has it's own esthetic.