I used to just sell off old cases and builds. Even the massive EATX towers with wheels (I remember that one cost me $75 to ship years ago).
I somewhat stopped doing that, for no real reason.
Still have (inactive)
1 Silverstone SG06 <-- Wonderful case back in its heyday. Didn't have the best airflow (partly due to its flawed 120mm front fan mount), as was endemic of early cases of that time,
1 Silverstone FT03 <-- A great idea, but with some minor space efficiency and accessibility quibbles.
1 Silverstone FT03 mini <-- They didn't learn a single thing from the SG05 and FT03. Last Silverstone product I purchased.
Recently pressed these back into service:
1 Ncase M1 V5 <-- It's a bit large, but very flexible and extensible. it's slightly large size is completely offset by it's incredible component density and space efficiency, IMO.
1 M350 (that was inactive for years) <-- It's not a great case, but with M.2 finally in full swing, I have finally found a use for it, along with my PicoPSU.
Current computer is in the:
1 DAN A4 SFX v4
Many, many, many sold. These include Silverstone SG05/06/02 cases, along with a beautiful, red, aluminum Lian Li mATX cube, countless mATX/ATX/EATX Antec and CM cases (including the P180 mini, my first case).
In the end, I am still thankful to Silverstone's SG02 (first "SFF" case in my possession) for bringing me to the SG05 (and to mITX).
While I do not find DAN's A4 SFX perfect, I do very much appreciate its extreme, unwavering focus to its core principles.
I think I will find a use for the SG06 eventually, but the FT03 and FT03 mini will eventually have to go. Shame, since I really love the vertical case concept.
What you said about the Ncase is so true. I remember when I bought it I was amazed at it's size but I was comparing it to the Ghost S1 I just picked up and it seems incredibly large. I am currently using my Ncase as a HTPC/Plex server with 4 x 3.5 HDDs installed and it is a wonderful case for this setup, like you say it is hard to find another case you can pack so much into the available space.
I have also been able to sell most of my previous cases, I usually do a hardware upgrade at the same time I do case upgrade and sell the complete setup. Cases I still have are:
Coolermaster Elite 110, my first itx case and still being used as a home pc for web browsing and video watching.
Ncase M1, which I am using for my HTPC/Plex server.
MI-6 which I just pulled my gaming build out of and will probably put up for sale.
Louqe Ghost S1 which I just transferred my build into but I have also ordered a Nouvolo Steck because I wanted to compare the 2. I have a feeling I will keep main build in the Ghost but I would like to hold onto the Steck because I am thinking about an AMD only build depending on how their upcoming components look.
Some of the itx cases I have gotten rid of, several out of shame.
Rosewill U2 Legacy (Jonsbo clone) sold as a complete build, still one of the most difficult itx cases I have built in and really taught me the importance of a "planned build"
Rosewill Neutron, a horrendously big itx case that was nearly as large as most mid towers. I think I bought this because the U2 was such a PITA to build in.
Phanteks Evolv itx, nearly as horrendously big as the Neutron. After the Evolv I bought my Ncase because I decided if I was going to have an itx case it needed to be SFF and was looking for something with better build quality.