Audio gear is not a good investment financially. It depreciates. Rapidly in many cases. No matter how much I love a piece (I'm an ARC fanboy) the used ones go down in value each year- and why shouldn't they? Caps wear out. tubes fail, pots get worn, scratches and bruises show up- it's that dang 2nd law of thermodynamics. Moreover new and better gear hit the market all the time. Add to that the digital revolution- a body slam to residual values!
Now if we classify investment as something that causes appreciation in ourselves that's a different story. My rig replays recordings that make me happy. What a joy to have a nice bottle of wine, turn down the lights and enjoy the music! It's often the best part of my day.
I have learned to be happy with "really good but could be better" and I do love chasing the gear- bit that's a luxury and not a necessity. Nor is it a good use of the time value of money. But I like it!