dippers are a virtual gimme on any of the small rivers in the area esp the eglwyseg.
In a couple of months there will be redstart and wheatear aplenty as well as a few cuckoos, but that doesnt really help you!
If your specifically after birds maybe head to the nth wales coast, flint & point of ayr are good, nice high tide roost at point of ayr. Or you could be on the northside of the dee estuary within an hour, burton mere, imf, good all year round!
If you're just after a nice hill walk in Llangollen north of the river is better: the panorama walk is good; or slightly west the llantsilios/moel morfydd area is gorgeous; or worlds end moors and walk south along the top of the rocks; or the horseshoe pass; or offas dyke path;
This time last year we had a great grey shrike at worlds end, and the year before a dartford warbler.
Further afield there is a gg shrike at clocaenog but maybe a bit far to go.
General things worth seeing in llangollen: horseshoe falls, crow castle, valle crucis abbey, canal & pontcysyllte viaduct, chirk.
Have fun!