Without kids I'd rather go to Brisbane than the GC, but then without kids I'd give both a miss and go to the Sunshine Coast! Plenty of decent restaurants in Brisbane, and a good city to explore. Train links are good, too. GC, I'd stick to north or south of Surfer's and avoid the bit in the middle (Surfer's itself, which is just too tacky). South - Around Burleigh Head is nice, with good restaurants. North - kick back on Tedder Avenue in North Beach and chill.
For a trip out (accessible from Brisbane or the GC), the hinterland is great to explore - plenty to do and see at Tamborine Mountain.