Not sure what happened with your booking but I have taken many cruises using the My Vegas rewards with no issues or complaints.
I have used the $750 off NCL on three bookings with no issues or complaints. Calling to book was simple, no upsells and quick and easy. The prices I booked at were the prices I saw online, exactly to the penny. My last booking the inside cabins were showing only guarantee available but the rep left me pick a cabin, that was very helpful.
These rewards have been great, especially since on my 3 bookings me and my husband were both able to use the $750 off saving $1500 right off the bat.