As Yglesias says, what would be really valuable for the future is building a national political consensus against torture and other gross violations of civil liberties. That would probably do more to deter future violations than imprisoning top Bush administration officials. Torturer presidents in the future can stack the Supreme Court with Bybee types who will help them get off scot-free, and torture without risking legal punishment. But you can't stack the American people. If public opinion is solidly anti-torture and your political consultants freak out when they hear the word, you're less likely to commit abuses.
But I don't think that we're going to be able to establish any such consensus anytime soon. It used to be that we were worried about Fox News defeating us in elections, or beating the drums for another Bush Administration war. Winning by big margins is nice, because we don't have to worry about those particular horrors for at least a little while. But now we have to worry about how Fox and the rest of the right-wing noise machine are going to continually sustain a substantial minority of crazy people, preventing the formation of an anti-torture consensus, an anti-war-of-aggression consensus, and anti-warrantless-spying consensus. Even if there's majority support for these views, anybody scrapping for power within the Republican Party will find reason to oppose them, just to get a majority of Republicans.
I think the impossibility of consensus on these issues is part of why nobody thinks about consensus and there's so much left-wing attention to judicial punishments for the perpetrators.