Hi Dan,
Newboy is right, the majority of the inshore wrecks around the country are fished out. You may find pout, wrasse and possibly a few bream on them, but generally not worth the effort.
Your time will be best spent either picked a good forecast and heading out to the 10-15 mile wrecks (Im still waiting for a window this year!) or picking reef marks.
But then again,...what do I know - wrecks are underwater obstructions, which in turn attract fish..so give it a bash and see what turns up.
Anchoring correctly is crucial to fishing on the wreck..a plotter is of great help. Drifting allows more chances of drifting directly over the wreck..but again a plotter really helps.
Adam