I have to admit, Steve's vocals are always well done and welcome in the performances and he seems to know the words to the songs (my downfall!). The "Old Joe Clark" rendition was great and really got the audience rocking. In fact, I had an extreme urge to join in on the mandolin. Gerry and others have added vocals in the past and I think they were all done tastfully as part of the total performance. Perhaps in the future we can all try to add some harmony!
On the other hand, some months in the past, we were serenaded at least twice by a group where the "lead singer" sang all of the known (and some unknown) verses of "Amazing Grace". The way it was done "showcased" the singer and left the "band" in less than a backup position. That was far too much singing and very little instrument music.
ie, a blend of both is great and tasteful.