I forgot to post this earlier. After a couple of comments on the windows, I went back to using the EXR, but added in a distance-from-camera variable to control blending to just solid colour. This way, when the camera gets close enough you can see into the rooms, but from a distance it's just lit circles, which looks massively better. I still need to tweak the distances where this takes place, but you get the idea...
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Formerly furswift