Jon, one preference I have...not sure if it fits with your ideas of scholarship and completeness...

I REALLY like to read the words to a song as I hear the embedded tune. You mentioned Lesley's site. She does this as well as Barry's tunebook at her site. I think this makes the site much more user friendly, thus accessible to those of use who are not familiar with the various songs. So many songs that people here are familiar with, I heard for the first time at Lesley's and Barry's sites. If I had not had the words and tune at the same time, I probably would have missed them.

I like your idea about related tunes. I've enjoyed Lesley's Child Ballad site for that reason.