Method for measuring the 'similarity' between FSA grammars?
you might have more luck from another angle &amp; looking into research into music piece similarity, there are researchers studying that, and while your approach can work, there are other approaches. there are large databases that look at many elements/ criteria such as lyrics, genre etc. eg Music genome project.

sometimes when theres a wide variety of algorithms a survey can help. here are two surveys on graph matching.


Matching Structure and Semantics: A Survey on Graph-Based Pattern Matching
Brian Gallagher
Graph Similarity and Matching / Zager