I think Meljor used a similar way to store his cards. He might have some additional tips for you perhaps?
I store them differently, but then again I alloted a lot more room for parts storage.
For parts I use a lot (often my standard testing parts like PCI graphics card and some memory modules), these are in a separate box on the desk.
Storing ISA cards I think does require a bit of care, since they can be quite long and one wouldn't want flexing resulting in cold solder joints or other related intermittent problems.
I've also found that storing the cards in opposite directions (so every second card has the slot bracket facing the other way) allows you to fit twice as many cards into the same space. But of course my priority is fitting all the cards into the available space, and not about showing them off!
I also find that open displays end up collecting a lot of dust which requires cleaning, whereas having the cards in a closed container keeps the dust off them so they're ready to go when I next want to use them.
When storing cards which are touching each other, please be wary of them not scratching against each other as some parts may get ripped out or bend when trying to get a card out quick. Theres always the danger of a moment of slight impatience, which may end up with you ending up with a useful card less in about 5 seconds time 😜
The dust is a main reason for me to store everything covered up. Or at least in an antistatic bag. If I (for whatever reason) leave parts on the desk or somewhere else uncovered, I made a habit of laying those down upside down, so the dust collects on the backside of the PCB and not within ISA/PCI/AGP slots etc. This is also better as I sometimes forget what I was doing or stop while in the middle of a project and then find the parts 3 months later 😊