One of the things Downie does poorly as an agitator is that he himself is the guy who usually lets stuff get under his skin. Lemieux was an agitator, no doubt, but he very rarely lost his temper out there. Again, I just don't think it's a good comparison. If you want to compare Downie to a player on that team, you should be aiming squarely at Chris Simon. Simon was a guy who could play on a scoring line, pot some goals, and was plenty tough. He also took his fair share of dumb penalties.
I don't think this team misses Downie's toughness at all. There's plenty of grit on this roster--they're by no means a soft team up front without Downie. Keep in mind the offense more or less dried up after Tanguay went down and Parenteau went cold, not when Downie was traded.
However, since you brought up Lemieux, one thing he did the Avs could sorely use is a guy who can pot the ugly goals up close. Lemieux could take punishment in the slot and still get to the loose puck and pot it in. We could use a guy like that, especially on the power play.