if it was me, I would start with some basic shapes, smudgy ovals and so forth, composite a few layers of them, and then run Make Kaleidoscope Image to achieve a sense of symmetry. I'd pattern a bunch of those results at somewhat random distributions.
I would vote for showing warnings, since Vuo currently has no 'compile errors'. There are increasing versions of this this, but if we can say, in some cases, a node definitely will never run, then that could be incredibly useful. We could build from there, for example guiding the user with suggestions, making Required ports visually different, etc. etc.