Steen at that point had a good rookie year and promptly went down hill every season afterwards for the leaf and was generally a guy who had potential but wasn't putting it together for the leafs. Coliacovo was an oft injured defenseman who you pretty much just wanted off the team because he played all of 110 games over 4 seasons with the leafs not counting his first 2. Oddly the reason we went for a 2v1 deal is because we had so many injuries and needed bodies.
Stempniak was a pretty good player with potential who had a 50 point season his sophmore year and had 13 points in 14 games to start the season he was traded. Honestly I went out of my way to watch leafs games those 2 seasons just because I was a fan of Stemps. He wasn't your problem and takes way too much heat from leaf fans just because of how the trade turned out and how bad your team actually was during that time.
It was a good trade at the time and if Steen stayed with the leafs its unlikely he turns out the way he did just because of how great he meshes with the system on the blues and its current roster.