I already proposed such feature: separate cargodist deifintion for express cargo class, but it was criticised because some 'bulk' cargoes such fish or coffee falls into this class.
Your proposition (to check TOWNGROWTH_GOODS, TOWNGROWTH_FOOD and TOWNGROWTH_GOODS) seems to be better. For example in case of FIRS, goods, food and fuel would be fall in these categories, it make sense.
Express sounds workable to me - if it needs to go express it probably is 'special' in some way. To play devil's advocate, I do buy at least somewhat dependent on the specific plantation it was grown on, and the specific roastery that roasted it. Similarly at the market I can make a choice be Atlantic or Pacific oysters, Scottish or Alaskan salmon, etc. It would not be that bizarre for fish and coffee to have specific destinations if user enabled it.