I can't see becoming a collector by accident. I thinks it's more of an obsession. Obsession is controlled by mind which leads to psychology. In a positive manner as some instruments retain value, especially with a rising cost of material and manufacturing. You buy a new car and the moment you drive it away from the retailer you're losing money. ( I'm sure you know this, and don't mean to teach you how to suck eggs). But by a new Fodera ( I don't know anything about them but saw this make frequently popping up on BC) and you can still sell it. The same goes for an aged Fender? I presume that even with inflation rate your profit margin sky rocket.
Is the psychology of collecting instruments an obsession? Yes, there that euphoric feeling when completing an online order or collecting in person. That unexplained excitement tracking the items movement by courier, unwrapping and even thinking what is the tune I will play first...
Are you a particular artist fan, absolutely, I've got to get the new signature model. E.g. things may sometimes get difficult here, I grew up and still fan of Iron Maiden, but don't have Mr McBrains SIT drum kit. It would take up the whole room.
Peer pressure, are you influenced by BC members, is there a competition of getting the better and more than others. This behaviour can be often observed in neighborhood. Sacha Baron Cohen demonstrates this in Borat movie, " this is my new neighbour......."
Investment, or something you wanted as a youngster but now you are financially able to fulfil your dreams.
I think , psychology behind collecting instruments is infinite , but what are the limits?