Let me try and provide a little insight into why you don't see many non-European hotel chains in Spain. Although I can obviously not speak on Marriott's behalf, I will pass along some comments that came up in a conversation that I had earlier this year with someone who has worked in several executive positions among hotels in Spain and now runs a consulting firm in the industry.
The Spanish workforce is extremely untraditional. Productivity is generally low, two months vacation a year is normal, and things generally happen at the employee's own leisure, not the customers'. Such a workforce would have a very difficult time adapting to a standards-based system such as the one in place at Marriott and at other major international hotel chains.
Purchasing is another problem - it seems there are very few centrally-based service providers that could supply the requirements of the hotel's food service operations in a traditional method, and none of them in a reliable fashion.
Although this sort of cultural barrier might be tolerable in a vacation-resort setting (ie the Marriott resorts in the south), it would be extremely difficult to run an efficient business hotel based on an American model in Spain. I do expect Marriott to enter the Spanish market in full force eventually (possibly similar to the way Marriott entered Canada... very gradually with a few token properties and then a high-growth expansion plan) when the workforce eventually becomes more productive and efficient. It is happening and don't forget that Spain became democratic (well, it is a monarchy, but you know what i mean...) relatively late compared to most other European nations.