Wish I had seen your post earlier. I wasted so much time testing duplicate finders until I found the MindGems Duplicate Audio Finder. I just recommended it here:
from where was pointed to this thread.
I totally love how good this thing is at finding similar songs without ID3 or any titles in file names!
Finding similar ID3 tags is very good too - it doesn't do just partial matching as even if words in the ID3 are rearranged it still recognizes that the title is similar.
My audio library has never been so organized 
I got the PRO version - it is worth every cent and has so many features.
Someone proposed the Similarity app above - I tried that tool too. It looks fancy, but it compares frequency histograms or something and produces way worse results and a lot of false detections.