I finally ordered something from Amazon.es.
I would say that their problem at the moment is stock levels -the two films that I was intending to buy were out of stock with an estimated re-stock date of 1-3 weeks. They only seem to have a few copies of most titles in stock (and that seems to be true of a lot of books as well as DVDs).
In the end I ordered two films that were in stock (I wanted to know what normal delivery times would be) and they were delivered three days later. Postage came to 7 euros (including tax), which is considerably cheaper than anywhere else I've used to import Spanish DVDs.