Wilco was already established as my favorite band when Nels Cline joined 2004. If he had not been added though, I can safely say I would not have seen them play 49 shows (currently). 34 since he joined crew.
A very insightful interview here, including the crossroads he was at when Jeff Tweedy put out the call.
Having seen Cline previously with The Geraldine Fibbers, I had zero doubt that he had the chops for the gig and thought he would mesh. Turned out even way better than I could have imagined.