Restaurant is at the Sheraton Mirage, 71 Seaworld Drive (along the spit, not far from Seaworld).
50% off deal is valid for bookings made via Dimmi, by 4/5, for lunch and dinner sessions until 9/6 (excludes 10/5 & 8/6, and Saturday dinners).
I'm told normal prices are:
Lunch $64 Mon-Fri / $79 Sat-Sun
Dinner $79 Sun-Thu / $85 Fri-Sat
Urbanspoon rating is currently 82% from 92 votes. FWIW I've been there once myself in Aug 2013 on another deal (less of a discount) and enjoyed it.
This place is excellent. Best buffet I've had in QLD so far.