I think the first question is whether you are want to visit a 9th century church in a monastery nestled in a valley. I think it’s beautiful, but some aren’t drawn to it. If so, that would mean walking down to Oviedo from Villaviciosa. The church at Valdediós is a very short well-marked detour off that path. I’ve attached some pictures. There is even an albergue at Valdediós, run by a joyous group of nuns and spotlessly clean. Very under-utilized. Valdediós is only 9 km after Villaviciosa, though, so it you sleep in Villaviciosa, it’d probably be too short. Sleeping in Colunga (there’s a very nice hotel rural there, where I slept years ago) makes it a 26 km stage to Villaviciosa, and then two day more into Oviedo. OR, walk from Villaviciosa, visit the church, and then go on to either Vega de Sariego or Pola de Siero.
There have been other forum threads on this topic. Check here
, and here.
The walk from Villaviciosa to Oviedo is typically a two day affair. There are good albergues, and the route has been put mainly off road. You enter Oviedo with a few kms of car dealerships and furniture emporia, but nothing industrial.
From Oviedo back up to Avilés is now a very well marked and pleasant, but not spectacular, walk. Avilés itself is a very pleasant stop. The historical center has been revitalized and is very picturesque and lively!
Buen camino, Laurie
and p.s., I agree with the suggestions about spending time in Oviedo. The pre-romanesque sites in Naranco are as spectacular as Valdediós.