Ah...keyboards and bass guitars, tricky one that.
I did run a few "acoustic nights" and did try to please everyone (mistake). I think there is a place for genuinely acoustic music events.
An electronic piano even if played quietly through its inbuilt speakers is just not the same as a proper piano. Take a reasonable piano (in tune) add a competent player and a merry throng, pretty soon you will have a group around the piano belting out "dirty ditties" at the minimum. Electronic keyboards are more convenient, stay in tune etc but they don't seem to have that same magic.
I went to one show where a very accomplished player had brought along her priceless antique double bass, the sound engineer absolutely insisted on mikeing it up so that everyone could hear it better.
Louder does not always mean better. She may as well have been playing a $30 Taiwanese copy for all the tonal quality that survived the amplification process.