I know what you mean. But if those values aren't intended to be used, I'd suggest to not let the user chose them using the slider or popping up a warning.
Anyway: Here are two different examples, which, I think, suffer from at least a related problem and don't make use of micrometer values
The first one is a simple rock object. Adding a power fractal to its surface results in a black rock, no matter what color, displacement amplitude etc you choose. The scale values are at
default.
The other example is a more complex scene. The min-scale is at about 0.5 cm... which is a perfectly sane value if you ask me. What really surprised me is, that it affects the sky too.
Also, I'd expect to have some weird polygons or something similar... not the colour changing.