I think that a fairer comparison would be "apples to apples" not "apples to Oranges". If you do not like a whole evening of mediocre to good solo a cappella singing, it should be compared to a whole evening of mediocre to good single instrument playing. It can not be compared to accompanied singing, with better or worse voice to instrument capeability.
I personally woulf by far prefer to sit through an eving of mediocre singing than mediocre instumentals.
I play well enough to piss off a lot of people who play worse than I do but I seldom inflict this on the paying public. I do however sing a cappela frequently, mostly with two other voices, who are both female.
In a crowded pub environment, I have never heard everyone stop talking to listen to any number of instrumentalists on any instrument however good they happen to be. I, and with my a cappella group have totally silenced the busiest of pubs with voice only.
Now! what really anoys me are groups like Crucible for instance who do both equally as well :)
JohnB