I'm gonna answer that second question first, because I can collect my thoughts on that one. I've known people who have sold their collection, and they had mighty collections. Then a year or two later they start collecting again. Only one person have I seen not revert back to collecting, but I think collecting ruined a relationship for him, so maybe he knows better or something. On several occasions I have thought about selling my collection and doing something more "productive", but the only "productive" thing I can think to do is to go back into game design, which wouldn't be bad. I've got the skills, knowledge, and tools to make games, and I'm an approved Wii U developer by Nintendo. I've just never done anything with that knowledge short of proof of concepts and prototypes. I usually get something working and playable, have some folks test it, say it's great, and then I stop working on it.
I don't think I'll ever sell my collection, but I could see one day down the line, getting fed up and selling off more than half of my collection. I was pretty burnt out with collecting... back in... 2014? Maybe it was 2015. I did most of my "online" collecting through a fairly prominent Facebook group, it wasn't a very good group, admins were always power tripping and scamming folks. Eventually I got fed up and continuously called the admins on their shit until I started getting banned from other groups because the admins threatened to ban their groups members if they didn't ban me. I pretty much don't do any of that group BS any more. I pretty much stopped collecting for about 6 months because of it. The main leader of that group is relatively local to me. So I stopped going to places I knew I might run into him at, because I have temper problems and the guy is like 4' 8" and I'd be too tempted to throw his Bobby Lee looking midget ass. He later opened up a shop another city over, he massively scammed hundreds of folks over stuff like NWC carts and stuff. I wanna say this whole thing was mentioned on some prominent podcasts. People threatened to kill him and burn down his store, so he shut down his store for a while, renamed the business, and now he pretty much doesn't leave his store and he sends his cronies to flea markets and stuff to get more stuff to scam folks with. Guy was a real Crook, fam.
As for burnout... Sometimes. Usually burnout revolves around one thing or another for me. I was pretty burnt out after playing through the entire Assassin's Creed franchise recently, I think I took a day or two and stopped playing games altogether and then I did a kind of pallet cleanser and played some random games. Sometimes I just get tired of playing altogether and I'll spend a day or two just watching Netflix or something.