For things to explore, we can always look at what is actually out there in the real world. For example:

Real asteroids are isolated from each other. Even in the asteroid belt they are on average a million kilometers apart. To some extent we already have these: Whenever you find an anomaly or signature that has asteroids its like finding one of these RL rocks.

Comets. Most are out in the far solar system and are single isolated bodies. There are most likely millions per solar system. Procedurally generated, they would always be a new discovery.

Rogue planets. Estimates range from 2 to 100,000 of these floating between the stars for every star. Imagine building some sort of scanning array for finding one, then having to fly out thousands of AU to get to it. By going from one to the next we could even get interstellar travel without gates.

Player built space stations. Let us build them at all sizes and at (almost) all locations and space will be full of stuff to find.

But we need stuff to be there to make it worth finding them. The content quickly become documented and repetitious if there is not enough of it and its not expanded. (Oh look is a type 3 rogue planet. The guide says we need to do X, Y, and Z to claim it, and then we get A, B, and C). A huge amount of content is a huge amount of work. A player can find, do, and document a site in maybe 1% of the time it took CCP to make the site.

I wonder if there could be a way for players to add missions and exploration sites to the game. That is I write a mission, CCP approves it and adds it to the list. I pay Aurum to CCP to cover their time. When any player does it I get ISK. Not sure if that could work....... but it sure would cause an explosion of content.