What are the results of the Djinn choices if you summon it? I have talked to it and received double my summoning cost back when allowing it to visit whenever, but I am wondering what the Karma impacts of interacting with it are as well as if the 'make me ruler of the world' option instant wins the shard for you.

There is a fork - you can get evil djinn and good djinn, and you can't guess which one before making choice.
Usually I choose "just talk", this either gives double cost back(evil) or +5 karma(good). It is impossible to get any result from"make me ruler", and evil djinn would steal HALF of your current gold/crystals if you ask for them.
For exact numbers you can look into event.var, 94-100 - evil djinn, 101-106 - good, and dialog.var entries 320+

Thanks. Sounds like I need to bite the bullet and translate a bunch of these VAR files to english for a better understanding of the game.