I'm not sure if it's possible to enable the 'Dimension' attribute (nor 'Resolution') to make it just as easy to add these columns to any folder as the "normal" ones. But if you want to add one or both to folders which don't display these attributes then:
- Temporarily change the name of the folder to any name that starts with the characters "Pictures" (case is important!).
- Add the desired column(s) you want shown as usual.
- Change the folder name back to what it was (or other name) and these columns should still be displayed the next time that the folder is opened.
Also, it appears these attributes will continue to show up in the list for that folder and can be hidden and displayed as wanted without having to change the file name again.
(Lack of extensive testing means it's possible that at some point or for some folders the method may fail but it seems fairly stable so far.)