Right now disks do not have the strongest visual presentation in the Places panel:
One quarter of the icon is covered with a green emblem that shows it's mounted. Taken together, the overall effect is muddy and visually indistinct. It's really hard to tell what it's supposed to be communicating to you. The situation is a little better if the icon is larger, but not by much:
I think there are two problems here:
First of all, the use of emblems on top of the icon to connote mounted status results in 1/4 of the icon being obscured. And at the default small size, the emblem's icon is indistinguishable; only its color stands out. We could probably indicate status with different icons rather than emblems on top of one icon, which would solve this problem. Or alternatively, we could use smaller colored dots as the emblems and forget about sticking an icon inside of them. Or only show the full size version at a large size, and fall back to a small colored dot for 22px and smaller.
Second, the drive-harddisk icon itself could stand to be improved. Particularly at the small sizes, it doesn't look anything like a disk. I see an old-fashioned CRT monitor when I try to figure out what it is. Also, the Plasma logo adds visual noise and doesn't really make sense to have on there because there's no connection between Plasma (a piece of software) and a hard disk.
I think a better icon could help a lot here, especially if it's less visually busy and sticks to the basics of communicating, "hey, I'm a disk!" For reference, here's the icon used in macOS Finder, which has a very similar Places Panel to our own also also uses monochrome icons: