No need to be sorry, you did a great job - and I can understand the issue of favouring FG-stuff over the BG quite well.
I think the thing that irks me about the BG is not even that much related to it's complexity, but it has more to do with the fact that it could be a good FG-tileset in it's own right. You could add black outlines to certain tiles and you'd have a tileset for a room of sorts, something you might meet a NPC in for example. And it could be easily expanded into more.
As for the BG itself, it's a bit tricky to explain for me, so I hope I'm making some sense:
As a BG the graphics look kind of odd because these "Wall/Ground-tiles" have all the size of 16x16 pixel, like you would expect them to appear on the FG and this feels odd since the BG is suuposed to be farther away so you would expect the wall/ground-tiles to be smaller in size.
Yoshi's Island is actual a great example of how to do it since the game features a few levels which have a BG which looks like it's "a level" as they feature some grassland-platforms, sometimes even with enemies but all the graphics are much smaller in size compared to how they are appear on the FG so you can't confuse them in any way with the actual FG.
Edit: I also just saw your BG with the smashers on the other thread... and it's absolutely epic! I could see myself definitely using it, but... like that other BG, not as a BG. Again, this could be easily used as is as an absolute terrific FG-tileset!