I own one acoustic guitar, one electric guitar, one banjo and one uke. So I'm a long way from investing in a new instrument for each song I learn; that's pretty modest going for a strings player. The vast majority of what I play is on the acoustic guitar. (in fact I should probably sell the electric - haven't played it in over 15 years)

It's probably more that I've got a redundant arrangement that doesn't suit the material but I was just wondering. There's a big difference in sound and atmosphere, for example, in playing something on a mandolin compared to playing the same arrangement on a bouzouki or octave mandola; there's a big difference in sound and atmosphere in playing something on a steel-string guitar as opposed to a nylon classical. I've even found certain songs just seem to 'make more sense' when I've played them on the Baby Taylor guitar at my mum's house, compared to my own all-mahogany guitar.