Spain is great for cycle touring, very quite (compared to the UK) back roads, considerate drivers and fanatastic A roads that yes, have very wide well surfaced shoulders, these are also compartively quiet due to EU funded parallel motorways. Other bonus's that I like are plentiful rooms that are so inexpensive that I don't have to take camping gear (weight) and most villages having a drinking water supply for travellers.
I've done Asturias, Cantabria, Catalonia, La Rioja and Andalucia, C2C has always been a dream for me and this June I am doing Bilbao to Malaga via Santander, Salamanca and Seville, part down the Rua del Plata.