This is the web site of some friends of mine just up the lane from me.It's fully booked arround the Wales run though.
But the 'Things to do' 'The area' and 'The history' might be good pointers for you.
As Beavis said Llanberis,Portmerion,Beddgelert (need to read the myths/legends) Caernarvon,Harlech,Criccieth all very pretty.
But I'm biased as they are local.
If you do the A5 from Capel Currig to Caernarvon do it at dusk/dark when the helicopters go bobose.
Zeds love the Llanberis pass.
Free tea and car washing at my place if needed. Just 5 miles from the Evo T.
http://www.acottageinwales.com/