Sounds like you've got a good handle on it now. But just to throw a little more gas on the thread.
One thing that is not brought up often enough in the whole DX - cropped FX conversation is that slapping a 200mm lens on to a DX body (for example) may give the field of view of a 300mm lens but it doesn't give the perspective of a 300mm lens.
Same goes for the parallel scenario where you crop a FX image shot with a 200mm lens (again just for example) to a DX field of view equivalent to 300mm in post. Yes you've cropped the image area down to the same size as a DX body would have but the perspective of the image, like relative subject to background distance (which can effect characteristics like bokeh), remains the same as it would be at 200mm on DX or FX.
In a lot of cases (such as when there isn't a significant difference in subject to background distance) this wouldn't be noticeable but in others it certainly would be resulting in a different creative effect.