Here's a setup that would give a purpose to advanced spaceships a purpose without making the less advanced spaceships useless. The standard spaceship would only be able to go between a planet's surface, moon(s), and space station. It wouldn't be efficient enough for long distance travel. The spaceship mk2 would be much larger and more efficient (perhaps using a warp drive of some sort), but too heavy to reach escape velocity. It would have to be launched from a space station (maybe from a 5x5 launch pad) and could only go to the space stations at other planets in the solar system. mk3 spaceships would be MASSIVE and would allow you to go to other solar systems, but would have to be launched from a space station outside the Kuiper Belt. Extrasolar planets could be randomly generated similar to the way mystcraft does it, but with the addition of randomized gravity and atmosphere and the removal of cave, skyland, and void worlds. Why you would need that many planets, I have no idea.