Really like the changes you have made. Extra detail brings it to life, and those sacks are perfect for a overflowing post office this time of year. Nice job with the roof underside, good you've managed to keep the colour coordination going with the hinge which I think looks great. If you are open to suggestions I have a few thoughts..
If you can fit in a chimney this would be a big help for Mr Claus and would allow you to include some LBG, LEGO's best colour.
You could also include a standard LEGO spruce tree (3471) or two outside.
The outside lamp looks to me to be installed a little low, maybe if it was one brick higher minifigs wouldn't bang their heads so often. Alternatively it could be made a little less part-heavy although I do see the plus of the old look you are giving it.
The post office sign could be made in one line to facilitate the above, unless you are a big fan of big signs!
The arch over the door seems to be one brick too low meaning an inevitable lawsuit from a tall minifig someday. I see the complication is in the staggered use of masonry bricks so not sure how you could easily fix it and you probably considered this already. As you have not used a baseplate you could actually take off the floor and build down. Would need you to lower the window and do some tweaks but would be an option.
Of course these are all subjective points so you might not agree with them. You can take them with a large pinch of salt ;)
Overall I think this is a great MOC and its great to see a MOC evolve and improve. Look forward to seeing more.