To quickly tac-onto the last post about players vs difficulty...

Serpent Spawns quite a distance away from people at night or in storms (day/night) and will hang in that area until they are removed. So if you have an active server with fast ships, expect more and more serpents than a solo player lol

So that is i suppose one way i know of that having a high number of players (esp independent ones) will increase difficulty without knowing. But i am pretty sure that is it outside of the bosses.