1. Ships (most) should always pick the shortest path
2. They have the effect of making the emperor feel better :) (in theory) They also attract traders, so there is actually a positive side already
3. Yes, when a high level imperial employee dies, they get a "Ghost Ship"
If the imperial tombs only make ghosts, what are the requirements for an empire to spawn a warden after they fall?
Also I meant, can ships plot new starpaths entirely?
Ah good question, you will be the first I tell :) Wardens spawn only for empires which have controlled the galaxy, and even for the it's only a 10% chance once they die.