Selling seems to me to be as important as buying, when it comes to actually producing great images... Remember clearly when I ditched all of my Canon gear (a lot) in 1994, and bought a a second hand M2... The feeling of letting all the options and security go, and then just having to get things done with minimal gear - I learnt a lot, and it made my images that much better!
Currently I am quite bloated equipment-wise, and just today I realized just how much it has hampered me when it comes to actually producing something. On the other hand I had to go this route, as I am getting into modes of photography that I have not tried before (static medium-format things as an example).
It feels great shedding old stuff! Perhaps even trading it in for a ticket to go somewhere new, and use the equipment that I have kept, and actually need. Which is often not much - these times an M8 and some lenses, with a Mamiya 6X7 for some specific projects.
Selling is clearly under-rated!