For me, it's the one that stopped all of the churn buying, selling, window shopping, over-analyzing and what-if'ing.
When the guitar speaks to you, when you can't stop thinking about grabbing it for just a little more practice time, when you feel the sense of awe upon opening the case, the beauty of even a single note...these sorts of things provide real and lasting value.
My guitar is expensive by many standards, but it put an end to so much other stuff that the benefit is significant.
I love my guitar. I hope you love yours too.