I saw Adam Clayton switch bass on almost every song when U2 played in the football stadium here in Houston, and you couldn't hear the difference. Kind of pointless. I watched Joe Bonamassa switch, just about every one of them a Gibson Les Paul. Not a lot of tonal difference there, either. Carmine Rojas played the same First Act bass all night and sounded great. But sometimes there is a reason to switch, I saw of Porcupine Tree last night and Colin Edwin played four basses, a fretted and fretless Wal, a Spector Euro 4-string downtuned to C, and another one (I think a BassLab Soul fretted 4-string) that all had distintive qualities.