Also, if I cast a spell on myself that is positive, don't I then get three positive spells targeting myself?
The problem is that it just straight up doesn't work. It's not something that makes sense from the rules.'or if there would be no effect to you' was an attempt to prevent abuse with white removal such as Dispense Justice as otherwise you can force your opponents to sacrifice twice the usual amount of creatures with no cost to yourself. It is poorly worded now I look at it, though.
What you were trying to do was probably:
Whenever you cast an instant or sorcery, each player copies it. Each of those players may choose new targets for their copy.
Though that runs into similar problems as hivemind.