Tom,
I have been to the area and played there a few times. Not a dream in terms of GCA and I wouldn't recommend going there just for the golf. The Canary Islands are further away than most people think: a 3h flight from mainland Spain and around 5h from London/Paris plus transfers. The weather is certainly the best in Europe in January (mostly because the islands are not in Europe...) and it should be 22-25 deg celsius. Temperature there is always the same year round. There are two major islands: Tenerife and Gran Canaria where golf is concentrated and the minor islands are harder to get to (except Lanzarote) and mostly don't have golf (Gomera has a course, but that's it).
In Tenerife you have Real Club de Golf de Tenerife, which is the older course in the island. The rest are touristic/resort layouts which are quite hilly and not so good. Abama (Dave Thomas), which is displayed highest in the ratings can only be played in a cart and is the most severe golf course I have played: all built on the hill of the Teide, the island's highest volcano. It has nice views and that's it. The second best ranked course is Costa Adeje, which is close to Abama. Its better, as it can be walked, but I find it a quite ordinary layout. I haven't played the other courses, but they are supposed to be worse.
In Gran Canaria there is better golf than in Tenerife. You have Real Club de Golf de Las Palmas. Designed by Mackenzie Ross and built on the cauldron of an extinct volcano, it is a nice course with some good holes. The other good course in the island is Maspalomas, also designed by Mackenzie Ross and located among a protected dunes landscape in the south of the island. Haven't been there for a while but it was also ok.
In my view the rest of the Mediterranean coast (Alicante, Costa del Sol, Valencia, Cataluña, etc.) and Algarve, is hit or miss in January. The better chances are in southeast Spain (Murcia and Almeria), but most of the golf courses over there have been built during the real estate boom (10-15 years ago), so mostly residential developments with no real interest in terms of GCA. I have played a couple of Nicklaus Design layouts (Hacienda Riquelme, El Valle) and the three courses at La Manga Club (Robert Putman). Reasonable golf, but not sure if worth the effort of getting there....