I kinda had the same issue...From Regina to Puerto Plata Staying at a Riu resort we are paying with tax $1605 for 1 week all inclusive. We are going mid February which is high season but most of our friends think it's to expensive. All our family has put down the deposits, but no friends who say they are coming but wanting to book last minute to get a good deal. My travel agent has advised against doing this because first out resort has less than 500 rooms, so they will fill up quickly and also if they do fill up really your guest can't come to your wedding if they are not at your resort. I know our resort requires 80% of guests to be staying at our hotel or they cannot come.
I would really try to encourage people to pay ahead of time, this is not just a vacation this is your wedding. I feel that for our situation, the people who truly cared about us have already booked.