Absolutely. That's one part of it. Some of the issue is demographics causing a supply and demand imbalance. The Baby Boom is a huge number of people, and they are aging and some are selling off their old stuff. This is going to continue. The Millennials aren't to an economic point that they can afford much in the way of luxury items, and they can't afford the space to store much of anything anyway. The population dip in between means that the supply will exceed the demand for another ten years or maybe more. The Millennials will get around to prosperity, but they have generally come of age in tough economic times and are economically damaged because of it. Economic recovery, whether it touches everyone or not, won't solve this supply and demand problem until a large number of new people have the ability to buy musical instruments and the interest in buying them.
Where I see this connecting to the state of musical instruments is that I don't think Millennials will have the same desire to buy physical instruments in the same quantities that their parents and grandparents did. Being a "rock star" is just another busted career path to them. It is a lot of work, almost zero pay these days, and may look like a relic of a bygone era to them. My step-son said music with real instruments sounds "old" to him. For kids coming up these days there isn't much of an incentive to learn to play an instrument. Once they get that disposable income (which they have plenty of as the scions of the over indulgent gen-xers that buy them every electronic gizmo) they probably won't buy guitars and basses with it. They will by software and sequencing equipment, maybe some microphones. For them a Jimi Hendrix is a funny looking dude in a video game, not an idol.