Only wear shorts at the beach
If you don't care what people think or don't mind standing out like a sore thumb, wear shorts. As mentioned by others, nice restaurants, clubs, churches, and historical areas of interest will not let you in. In tourist areas, about anything goes except for what I have previously mentioned but if you feel more comfortable wearing shorts, wear longer/blue jean/casual shorts not the cheesy bermuda type. I personally like to fit in as much as possible and always wear long pants, blue jeans during the day or docker type of pants with short-sleeved collared, button-up shirts that are kind of dressy. I only wear t-shirts, sandals, and shorts at the beach. Even in Boca Chica where 90% of tourists are allowed almost everywhere including the discos there wearing shorts, I dress like I would going out to a club in the US. I never wear tennis shoes, always leather shoes similar to dockers that are not too dressy but my day attire will let me enter almost any place in Santo Domingo. When I go sightseeing during the day, you might want to go out dancing, etc and it is a hassle to have to go back to the hotel and change. Plus if you want to hit on a nice girl she won't be embarrassed being seen with a tourist looking like a fool, I'm saying this not knowing if you are single or not.
I have never seen a person in 1st class wearing shorts but who knows. I have never flown 1st class but do notice about 1/2 of non dominicans flying into the DR, in coach class, wear the cheesy tourist garb.
dale7(Howard)