Well, it certainly makes good sense for community singing. Our song circle has certain members who never seem to be happy with the standard version of a song. They want to alter the tempo on the third line of each verse, or put a little swing in the song, or use alternate words. All this may be fine if they're singing solo or with a group of musicians who have the luxury of practicing - but they end up with chaos when they try it in our group of non-singers who are just there for the fun of it.
Wesley's rules make a whole lot of sense for community or congregational singing. I've come across many church music directors who scoff at Wesley's rules. Their choirs may sound terrific, but their congregations can't sing. Hooray for Wesley!
-Joe Offer, Roman Catholic-