In terms of passenger numbers, they are down over the past 3 months on the BHX route by -385 passengers but they were in isolation up in September by +185. For BHD, they are marginally up by +115 over the past 3 months (July/August/ September).
I doubt if car parking charges will really have an impact given that you have to pay these at both Aberdeen & Edinburgh plus the cost of driving to these airports anyway.