Now I need to find this one particular world buried in my files some time ago and give it the Handbook polish.
In summery, it's a very pleasant garden world with ground and floating cities. TL 15 with an A port. Thing is, you need special permission to land on the surface ports and they are very draconian about trespassers. The world population is in the millions. What you don't see are living laborers. Whether you see them or not, automation serves the elite. Vast robotic armies and system ships guard and secure the world. Robots build robots. All manufacturing and economics are handled by expert systems.
Where are the normal people? As the technology of the world rose and robotics became commonplace, the upper class slowly replaced the population with automation at all levels with the riches of the world always going upward. Poverty and an uncaring elite caused massive death over time. To speed up the removal of the lower classes, the ruling bodies became 'generous' and sent huge numbers of people to nearby worlds as refugees and the robots removed any traces of their habitation to be replaced with terraformed lands of natural beauty and grandeur only appreciated by the well to do.
Tourists can stay at the starport and take in the spectacular accomplishments the inhabitants are proud of. Other worlds still trade for goods and services of a vast robotic culture though some share a distain or even hatred for how it was achieved but can't do anything.
Oh, I need to find and rebuild!