After reviewing "The Power of Sushi" I am still unsure of when to spread and when not to spread Sid to your own cities. I get that you probably shouldn't spread it to a foreign civ even if they have very few proper resources. I almost never have a great merchant lying around to use for Sid so I have only created it once before and I died very quickly in that game so I never got to spread it much. I have created Sid in a monarch game (Ragnar) and spread it to two of my 14 cities. I have enough resources to give 6 extra food per city. Is there a reasonably simple set of rules to determine which cities to spread Sid to or just spread it to them all? The only downside I can see is the cost which won't really bug me much.