I assume you are have seen this?
http://www.swbg.co.uk/I've only ever dabbled at Caswell before there was a bouldering guide, some quite nice stuff.
The Trench is quite a hike from Gower, although it depends where exactly on the Gower you are basing yourself. Theres some nice stuff at Rest bay at Porthcawl, although it tends to be either very easy or very hard - need a low tide though.
I guess some of the big stuff at Giant's Cave could be done DWS style, athough not sure about water depth! At high tide I have had a play on some of the stuff on the lower tier (King Wall) Lewes Castle at Fall Bay. Although it's a bit slabby the grades are easy and you are unlikely to fall off, but could jump safely. I know martin Crocker did some big DWS routes at Ogmore, but knowing him they probably aren't the safest or most solid.
Caswell Bay is known for having a fairly hardcore local crew of surfers, I have only surfed there once or twice though, and never really had much hassle. Llangenith is a huge beach that catches any swell going, and you can spread out and avoid any other folk quite easily. Do you have your own board? If not PJs is one of the few hire places so get there early if there are good waves.