It's the rest of the stuff that can go. I helped a friend move last month. After we'd been to the 5 places she kept her stuff, we discovered she had 5 coffee machines, 5 cutting boards, 5 juicers, etc. etc.
The things you describe make you happier and are not stuff. The things I described are just stuff.
Storage unit rental, now that's a means of preying on people who can't let go and/or move often.
(It strikes me that there might be startup value in "home inventory management", although it would have to be made as frictionless as possible - wave a camera round your kitchen, inside all the cupboards, get a list of everything you own. Snoop your Amazon webpages so it can remind you not to buy things you already have.)
[0] sortly.com
Were the rental costs a waste? I suppose I would have saved a few hundred dollars if I could have just gotten rid of the stuff earlier, but it would have felt like a personal loss instead of a natural detachment.
But what if it doesn't make you happy AND selling/discarding it makes you unhappy?
I suspect that hoarders are not necessarily happy with the stuff they collect, but they would become unhappy when they have to let go of it.