I am sure it is very common. I don't grow attached to material things, only with tools that I find them useful. As long as I feel that I don't use them anymore, I sell them. Of course, I am not rich and getting some money from items I don't use anymore is always nice. I sold my 500L F4 IS mark 1 few years ago, for just under $6k. I sold it because I got a bit tired of bird photography in NYC. Is NYC....only so much exotic birds one can capture. I used to have tons of gear. Now, I am shooting with a $500 Nikon D7000 with 3 consumer lenses worth no more than $200 each. 2 of them came out more than 10 years ago, AF D lenses.
In your case, you can downgrade your body for something older and cheaper and only keeping 1 or 2 lenses. Sell the rest.