If the Human couldn't do the same stuff that the Yeerk did, then he'd have to step down. I'd say the Human should keep the money, assuming the Yeerk would leave the planet or become an animal nothlit. Not much use for US currency that way.
The Yeerks betrayed the Andalites because they wanted better hosts, but for whatever reason figured there wouldn't be enough voluntaries to go around. I'm not sure why, though. I mean, say you're a Gedd controller. You're a Yeerk, and controlling another body is natural. Your semi-sentient gedd is trained and assuming you treat it well the two of you would probably get along just fine. Why wouldn't you assume that would happen with other species? Something made them think that if they got out there into the galaxy, that not very many people would want a Yeerk in their head. They figured it would be more efficient to conquer than develop really good PR.
It must have been the Andalite's disgust for them and their planet, but the details are fuzzy.