I do know that audiences, whether in concert or in nursing homes and festivals, like vocals better than just one instrumental after another. (An audience of musicians, rather than a cross-section, may have a different take on it) In one group I was in, the leader, a fiddler, wasn't interested in songs, only tunes. We rarely got the listeners actively involved.

Then the group members shifted, and with the new members on board, we started doing songs primarily, with an instrumental medley from time to time. Big difference- not only is our own enjoyment deeper, the audience dances!

I buy some CDs and tapes that are strictly instrumental but by far most of the ones I buy are vocals.