Well, you could alter this idea a bit and say that only a sending-off would result in a suspension for the final. So straight Reds as well as a second Yellow. That way the players would still have to refrain from committing "little" fouls, since two of those could well result in a sending-off. Add to that referees urged to watch out for this kind of behavior in particular and you've got yourself a fair alternative, I believe.
It's just such a shame when a quality player misses a final because of a dumb foul or something similar because he had collected one too many Yellows in earlier rounds. Not to forget that it happens ever so often that cards are awarded unjustly. Some referees are especially quick when it comes to drawing Yellows.
Xabi Alonso against Bayern comes to mind. Unnecessary foul, yes, but does he really deserve to miss the final for that particular tackle? I don't think so.
Edit: Thinking this through, that's actually exactly the same as erasing the accumulated yellows after the quarters.

So, I would like to see them basically do just that, with a lowered tolerance for tactical fouls and such to avoid players go crazy feeling all "invincible".