I agree that if it is an Iberostar that probably can put you at ease a little bit. We booked an unopened resort once just for vacation and it was amazing - we got a HUGE discount for booking before it opened and we never would have been able to afford the resort otherwise!
I think the biggest thing is to know yourself. Are you, what I like to call, a "control enthusiast" (control freak sounds so bad! haha)? If so, that just might push you over the edge. There are so many wild cards when planning a destination wedding - most of us have never been to our resorts before the wedding - and the coordinators tend to be pretty laid back about your day until a couple months out. That can be hard for many brides in and of itself, so add a NEW resort to the mix where it is hard to find past brides or reviews to help and it could be challenging for your state of mind. If you're a "wing it" kind of person and you can let the details go and trust that it'll all work out, I think you could get a really great deal. Even my resort (also an Iberostar) that does weddings every single day had some hiccups and issues so I think the resort being new will probably just be about the same! It won't be perfect, but none of them are
Good luck and happy planning!