I find Death Cab for Cutie an interesting case. I absolutely love everything from Something About Airplanes through The Photo Album. I liked Transatlanticism but it sounded to me like the band was restrained, almost robotic. Then Plans came out, which I couldn't care less about, but then all of a sudden they unleash Narrow Stairs, which I believe is their best album to date. With Narrow Stairs they've matured but managed to keep things sounding organic while avoiding self-parody.
Modest Mouse failed to do that with We Were Dead Before the Ship Even Sank, which managed only a couple of inspiring moments but failed to satisfy as a whole due to the ridiculous over-production and over-use of Brock's bark. I believe March Into the Sea and Invisible are the only tracks that really make use of the production, but I believe they still need to bring back Brock's sensitive side. One of my favorite things about Modest Mouse has been their fragility---Brock's barks were always balanced with his sympathetic, high-pitched croon. His screaming then had some effect.
I also believe Iron & Wine is a perfect example of getting better with age. They've actually gotten *more* interesting as they've expanded their sound. It's always nice when that happens.