I sold my original NES collection back when I was in college. Overextended myself financially and had to move home, requiring me to break the lease in my apartment, and selling it was the only way I could do it without ruining whatever credit I had (I was 19). I had over 400 games, many in box (Dragon Warrior 1 through IV mint in package, original Final Fantasy factory sealed. Those I sold separately). Each game had a Nintendo plastic sleeve, was always alphabetized, and taken care of. Made over $1,200 on the NES collection alone, adding around $400 for the Dragon Warrior set and $200 for Final Fantasy.
I wish I had that collection back again. I also had SNES and Genesis collections, but they were nowhere near the size of my NES collection. Made about $500-600 on each of those. From time to time I've considered trying to re-acquire the NES collection, as I'm in my 30s now, but with my NES Classic Edition hacked with all US released NES games, I can't find a reason to do it outside of complete and utter nostalgia and righting a stupid decision in my youth.