I research this topic. I'm a consumer psychologist and marketing professor at the University of Michigan. In the consumer psychology literature, there are two main explanations for this behavior -- one more positive and the other more negative. But they overlap and both have elements of truth to them.
The positive spin: variety-seeking behavior and intrinsic needs. Variety seeking behavior is a fancy way of saying people like to try new stuff. In one study, wine lovers were interviewed as they were buying wine. They were often buying new wines they hadn't tried before. They usually believed that they would enjoy the taste of the new wine less than their favorite wine at the same price. So why buy it instead of their favorite? The best explanation is that they got two different forms of enjoyment from the wine: one from the taste, and a second from the adventure of learning about new wines. So their favorite wine might be (taste = 9 pleasure units; new experience = 0 pleasure units for a total of 9) but the new wine might be (taste = 7 pleasure units, new experience = 3 pleasure units; for a total of 10). So even though they expected to get less taste pleasure from the new wine, their total enjoyment would be higher than if they bought their favorite wine. The analogy is pretty clear.
This also ties into the psychology literature on Self-determination Theory, AKA intrinsic vs extrinsic needs. The relevant point here is that people have an intrinsic need to learn and grow. Trying new things helps us do this. So in this light, swaping out your equipment is part of the virtuous endeavor of learning and growing as a person ;-).
in this type of explanation, listening to music is only part of the pleasure we get from our hobby. Contrary to the slogan that "it is all about the music," this theory suggests that it's partly about the music and partly about the pleasure we take in learning about and using the equipment itself. In this way we are a little bit like watch collectors for whom it's really not "all about just keeping accurate time." It's mostly about how cool and interesting the watches are. Some audiophiles don't like to hear this because it sounds crass and materialistic compared to the elevated pursuit of music as art. But we don't need to see it in a negative light. And we'll be happier if we are honest with ourselves about how and why we enjoy our hobby (and why we are reading this listserve right now instead of a listserve on music).
Negative spin: it's addictive behavior. To make a long story really short, this point of view says that evolution set up our brain to reward us with dopamine when we acquire a new useful resource. As we get into our hobby, our brain gets accustomed to these dopamine hits. Eventually, they become a motivation on their own in ways that aren't beneficial to us. We see this in all sorts of areas of life including shopping for all sorts of different products.
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Finally, please forgive my ending this post with a shameless plug. But if you're interested in these issues you might enjoy my book The Things We Love: How Our Passions Connect Us and Make Us Who We Are. It's widely available. It covers the psychology of why people love all sorts of things. But being a bit of an audiophile, I focus on music-related topics fairly often.
