There is nothing usual/common about it. Its expensive and its prepared just for fancy meals in DR. You are not going to see Bacaloa as plato del dia everyday, everywhere, no happening.
See post #38. Not sure why you think your Dominican experience, which seems somewhat limited judging by your posts would override that of actual Dominicans. Nobody has said it is the same as plato del dia simple that it isnt unusual nor a delicacy. Certainly my Dominican family dont think of it that way. It is simply fish to eat on fridays.