In all honesty, I've thought much the same as you've related here. Would Bill really want to be "First Man" to Pres. Hillary? And perhaps more importantly, would Bill want Hillary to potentially (in her mind) create a more stellar legacy than he? I think Bill gives her lipservice about what a fine president she'd make, but she's not all that smart, politically, and I'm sure she depends upon his political instincts. He'd figure out a way to torpedo her presidential run, without her ever knowing it.
Hillary is easy to motivate. Bill OTOH is a toughnut to crack(no pun intended). He is not motivated by too much other than getting away with something and he really has a strong need to rub elbows with the powerful, but yet does not want to be one of those same people. It's like he wants to be a go-between or consigliere. Bill is one of those employees who wouldn't be happy unless he was padding his expenses by only a little bit, daring you to find it. He would be one of those employees who would decide to attend important meetings based only on who was at the meeting, not it's substance. Bill is not a details person and would leave almost all assignments to subordinates to finish once it was no longer high profile. Bill feels that most his coworkers are borish and tries to sidetrack them to make work more entertaining.
Hillary on the other hand is easy.......All you'd have to do to wind her up and watch her go is to question her every decision. Not that you need to or want to, but without that she'd have no fire in her belly. She's too stupid to figure out how she was being managed. People like that are quite valuable in the workplace. You can get them to the point that they walk thru the door each day ready to rip someone's head off. It's loads of fun.