Opponents don't scale according to your level. I just hex edited a new game and being level 2 or 100 made no difference to opponent levels the couple areas I checked (first cell block, start of citadel, start of act 2). There could be certain opponents that adjust to your level, but I have not noticed this, and don't recall it being mentioned in the forum.
I only used the BF for the merchants, in part to prove the dungeons were optional (there was some complaining when the game first came out that there were not enough skill points and it was too hard if you didn't level up in the BF).