first of all, not true, there are lots of great bachata songs kingo 
secondly, id know id love a 100% bachata night, but there probably arent a lot of people who feel the same. i think its better to have a mix maybe a 70% bachata night
but thats just my opinion, i could be wrong.
i know i dont like 100% salsa nights, and i really love salsa. if you did it, it would be a brave move, and i wish you well.