Check out Boucher's numbers. Decent offensive numbers, but great +/- in his time in Dallas, even last season, when the Star really struggled. And when you talk about Turgeon, you have to look at the role he played. Most of the time, he was playing on the 3rd line, so he wasn't exactly playing tons of offense.
As for Koivu, I'm glad to have him signed. Not many guys these days stay committed to a team for this long.