I've also found that the same song played in different keys WITH a capo, therefore same position of chords, will sound and feel different. Just moving the capo up one fret has made certain songs come alive for me, especially going from the key of E capo'd up one fret to F.

I also agree with Easy Rider about different voicings on the guitar. When my husband and I do guitar duets, we (obviously) play in the same key, but different positions, usually one with a capo and one without.