I think you're absolutely right about rationality being pegged to the aspirations of the voter. I don't agree with the premise that you have to be comfortable with the status quo to accept the logic of choosing the lesser evil. It depends on your priorities and the underlying assumptions (or as you put it, aspirations).
For example, whether the Dems or the Repubs win in the U.S has major implications for reproductive rights and marriage equality. If those issues are critical issues to you, then that will trump more abstract reasoning about long-term electoral strategy. Similar arguments could cogently be made by environmentalists. You don't have to agree with those arguments, but they are valid and they can't be dismissed simply as fallacious (something is not fallacious by virtue of it being disagreed with or even by its being false).
Or, if you're a member of a struggling union that is fighting to stay alive, you might care more about preventing a Republican sweep than you would about paving the way for the Greens to have a shot at participating in the debates in 10 or 12 years.
Alternatively, if you, like me, do not have faith in the electoral system at all because of deeper underlying assumptions about the nature of political power, then it's hard to see there ever being any kind of option produced by it other than a lesser-evil. A choice of lesser evils is the inevitable product of a representative electoral system. That is not a manifestation of a centrist, status-quo attitude, but quite the opposite.
I'm not saying everyone should adopt a lesser-evilism mentality. Or even that anyone should. I just don't like it when ideologues like all the Matt_Heinses on this site refer to anyone with any kind of differing political opinion as "manipulating people" and "usurping democracy". That's the same "lalala I can't hear you" logic regurgitated by the right wing ideologues which contributes to the impression that we are all so wildly divergent in our interests that no kind of political compromise could ever be possible. Of course, any time someone tries to inject some nuance into these forums, the response is predictable (see Heins' posts above).