The reason to do it now has nothing to do with political advantage (except in a negative sense, as you state, probably). The reason to pardon him now is because it's the right thing to do.
There are times when you do the right thing despite the political consequences.
I admit that the President may have more information than I do about what the real cost of suffering those consequences now may be and I still trust him to make that judgement. He and Libby both would put off doing the right thing by Libby if it were to be at too high a price to the country.
I harbor the same fond hope as RodGuy911 that a pardon, now, would be the opening salvo in an aggressive campaign to stomp the traitorous bastards on the other side into the ground (my characterization, not his). And I certainly agree with him that it would fire up the base.
lets hope it actually happens.