3 nights? You'll never fit it all in... and this may be a little late but for future...
Where were the ship wrecks in the muddy estuary on the northern side? Dulas Beach?
Red Wharfe Bay is worth a visit
Rhosneigr is next to valley, has a restaurant - the oyster catcher, that trains the local youth. Good food, good cause. Not a bad beach either for the rocks and waves.
Breakwater country park has some good views, as does the Penrhos country park.
How are you getting there - where are you coming from? If possible, take the A5 from Wrexham, through Betws-y-coed...