Thanks for the advice. Where do I find the offer for the Hilton Amex? The only offer I found (linked from Hilton's website) doesn't mention anything about 30000 pts after spending $1500.

Although it would be nice to stay in an exec room at Hilton, I don't think we would pay $450/night for a hotel in Dubrovnik. Since we are both grad students, we don't have a ton of money to spend, but we are able to take some time off. We are planning a slightly longer than usual honeymoon (~3weeks) with slightly less luxury (we budgeted an average of about $150/night for hotels- not including venice). That is why it would be nice to spend a few nights at some nice places along the way if we can do it relatively cheaply.