On the subject of Pariston, it's just like Ging said, Pariston is like Ging and Netero. All he cares about is a worthy opponent. Having something to test himself against. It's just that Pariston likes to test himself mentally/politically.
Once he'd won the election, he didn't care about it anymore, because there was no one to oppose him, no challenge, so no reason to remain Chairman.
Interestingly, this makes Hisoka one of the characters that is most in-line with these character's motivations.
Yeah, all through this arc people were saying "he should just wish that she doesn't grant anymore wishes". It seemed like the obvious conclusion to come to...right up until they revealed that Something was a real person with feelings. Which immediately makes it a dick decision.