
It can be pretty random, as enclaves can be destroyed before you even meet them assuming you manage to find them. Keep in mind the game was created before the patch that increased enclave spawns (real life setting playtime limitations.) So, the question is: how much of the galaxy should I expect to have to survey before finding anything of the new fun stuff? I also don't think that any of my neighbours have gone out of their way to destroy any leviathans or enclaves that might have been there, because everyone I have met so far is very peaceful, and noone has near enough strength to take out a leviathan. There are, to be fair, some systems fairly close to me that I have not surveyed because of closed borders, but it feels like I should have encountered something by now, unless both the leviathans and the enclaves are ridiculously rare. I have NOT found any leviathan or enclave. This is fine, I expect I'm in the mining drones' area of space (but there should maybe be more than two systems with them?). So far, I have found two systems with mining drones, one with space amoeba and the Tiyanki paid a visit as well.

I used default settings, except that I use the non-clustered starts option. I started a game right after Leviathan came out, and I have now explored somewhere between 1/3 and half of the galaxy.
