Keep in mind that a CC provides 50 power, so that would be a negative power cost to build one.
Come to think of it, your third option sort of makes me misread the question. Rather than why or why not build an outpost, it seems to imply how would you build an outpost. By tubing, or by building an extra CC.
It also makes me wonder why I'm replying to this question, since I usually DO build extra outposts, if you consider tubing to remote locations as building outposts.
But then it also depends on just how far away you'd consider an Outpost as being. Often I don't build that far away, so by late game, my main base is at least enchroaching on the outpost, if not consuming it.