I have always used every working pedal in my pedal boards (as in, they function correctly, and aren't noisy). As a result, my boards contain a lot of pedals (see the other pedal-board thread for pix), and I try to use them all regularly. I wouldn't ever sell an unused pedal - I bought it for some reason, and unless I truly would never use it again the resale value probably wouldn't be worth my while.
However, I don't have in total as many pedals as the OP has spare! I suppose if I had that many spare pedals I'd want to display them or at least have them really accessible for swapping out. 40-50 spare pedals, at an estimated $150 per pedal (which is probably low), is $7000-ish tied up in idle equipment - although maybe only $5000 if liquidated on the used market. If I had that many idle pedals, I'd seriously consider whether that cash would be better used towards a PS purchase or similar...but then, I might say to myself, why have another pretty guitar when I can have all these cool pedals?!
There are a bunch of pedals I can see there that I'd want on my pedal board(s) - the Echorec, the Belle Epoch, the RAT, the AquaPuss, etc, so I'm fascinated to know what the OP has on his active board right now...