I am trying to be a bit humble since my experience is definitely limited, but to be clear, I do have
some experience with an XT clone at least. Still, I haven't written very much code targeting an XT machine, and especially, I have never mucked with CGA beyond BIOS routines. I've got to imagine that even Commander Keen had to be doing some pretty hot tricks, even though the only novel technique I'm aware of is the EGA adaptive tile refresh one, not anything CGA.
Of course, it's never too late to write some wares for XT... I'd prefer to get an actual XT for that, though. I'd fear that if I only ever tested on emulators or clone machines, I would end up writing code that doesn't work on any actual XT :)