The following is mostly written about guitars and basses, mandolins and banjos, but could be applied, to some extent, to every instrument… Except for the Bassoon - I don’t see the appeal of an instrument that looks like a shisha and sounds like a farting drainpipe.
The reason I repair guitars, even when I’m not getting paid or particularly interested in the work is because I believe that guitars are made for playing. Guitars that aren’t being played aren’t guitars, they are guitar shaped objects – things that adorn a wall or fill a case – they aren’t complete anymore. It’s like the distinction between a living, breathing person and a cooling cadaver – they are made of the same parts and are for all intents and purposes the same thing, but the latter lacks the spark that defines the former.
Many people have guitars that live in cupboards or attics because they’ve got nicer guitars or consider their guitars to be unplayable, I don’t approve. I know it is a heretical suggestion, and many a guitar nerd would dispute this, but I don’t believe there is such a thing as an unplayable guitar. I have yet to encounter a guitar that wasn’t, with a certain amount of work, playable. I’m not saying that people aren't justified in replacing the guitars with something better, nor am I saying that I can make any heap of shite Encore play like a Fender or a Gibson. I can, however, make them playable enough, playable enough that playing them isn’t a case of man versus machine, which is enough for someone to learn to play on it.
If a guitar is actually completely beyond repair or so profoundly shite that nothing can be done (it happens, generally only with acoustics, they are more difficult) then I strip down the guitar for any useful parts, screws, pickups, wire, pots, jacks and switches, hardware of all kinds. It doesn’t matter if it isn’t very high quality, the key thing is that if you stockpile parts you can repair guitars for no cost, you never have to ask yourself if it is worth your money to do it, and so even the lowliest of axes can be brought back to life and passed on.
Some people have vast collections of guitars, largely unplayed, they may have reasons, they might sometimes want a certain sound that can only be obtained from a certain guitar other than their primary one – but I think that when someone buys a guitar they should ask themselves the same question people ask themselves when they buy a dog – they may want one, they may think they look cool, but they need to consider whether or not they can give the guitar the attention and care it needs. I have no problem with people owning more than one guitar, as long as they aren't part of a collection of instruments owned for vanity and not neccessity. I have two basses, a fretted and a fretless, I play them about equally – I did have another fretted (which had been replaced by the new one) I knew that I wasn’t going to play it much anymore, so I passed it on to someone who would – I have two guitars, an acoustic and an electric, I don’t play my acoustic much so I let my little sister play it.
It is these principles that I cite when asked why my guitars and basses are so strangely modified and upgraded, why they are so covered in switches & knobs and filled with peculiar electronics. I modify my guitars because I don’t want to have a heap of unloved, unplayed guitars around just so that I have access to the sounds I want. With modern amp modelling preamps and a decent amount skill you can make pretty much any sound you want with a well tweaked guitar and that saves wood*, money and storage space
*Don't get me started on 'environmentally aware' musicians playing something like 'live earth' holding an instrument made from mahogany or bubinga.