Spain is mediocre when it comes to topographic maps. Certainly beats Italy, but you won't find the quality of France, Switzerland, Germany, or northern Europe. They're not too old — you can find maps less than 10 years old in the new digital series, at scales down to 1:25,000. In general, what's on the map exists and is accurate. Unfortunately: most hiking trails are missing.
They can be hard to get outside Spain, but can be ordered online and shipped abroad (at least inside the EU). We order them directly from Spain. There are a number of stores selling them, googling for tienda mapas topograficos may help. For example, see Tienda Verde. It helps if you know some Spanish and phone the store directly, for some stores may simply ignore your e-mail if you write them in English. Even passing your e-mail through Google Translate improves the probability of success.
For hiking trails, you need to complement the maps with either:
- A good hiking book
- Online-downloaded trails.
The good news is that Wikiloc is very popular in Spain. Pretty much anywhere you'll go you'll find hundreds of GPS-trails. Even if you do not use a GPS-receiver, you can use those in combination with your map to find out where the trails are. It requires good planning and it's helpful to have access to internet while on your trip.
To get an impression of what the maps look like, use the free online tool Iberpix visorign. This is a pretty good tool to interactively explore topographic maps of all of Spain, including the islands. I think it's also possible to display trails with the IGN-map as a background, but I will double-check that. I will upload a screenshot tonight.