Kindly don't put words in my mouth. What I wrote was that the notion of equal marriages is , for the most part, an anacrhonism in today's world. That is, equal/dynastic marriages were made for political and legitimacy reasons. This is no longer necessary in today's world. Not only has the institution of monarchy evolved and changed in most countries, but the world is now more international. Rather than cementing bilateral relations and institutions through marriage, states now aim for internationalism through trade agreements & international conventions and principles. Thus my statement was a general statement based on the realities of today's world. Felipe or any other prince can marry whomever they want.
Moreover, whereas previously in some countries only the daughters of a small pool of elites had the qualifications to become the wives of powerful men, today's world there are many highly educated, capable, and competent women from all socio-economic backgrounds. The role of consort too has changed. I daresay women like Queen Silvia, Queen Noor, Princess Maxima, etc. are more suited to be a Queen in today's world than many royal women of yesteryear. In fact, many 'royal' women were disasterous consorts (Alexandra Feodorovna comes immediately to mind).
If there was an eligible British princess, or rather any other European princess in a ruling house, I'm sure HM Queen Sofia would have preferred Felipe to marry that girl other than the woman he is going to marry (there nothing wrong with the woman he is going to marry by the way).
How do you know that would have been her preference? Did she tell you that? In fact, she's stated otherwise on more than one ocassion, as have her children. I hardly think that Her Majesty is a liar. Sure, she wants her son to marry a suitable woman, but his happiness is no doubt also a factor. As far as eligble Princesses go, there have been several from reigning (they don't rule any more, I'm sorry to say), and non-reingning houses. The Spanish royals have married into non-reigning houses in the past, so I doubt that this would have been an impediment if the King and Queen were adamant on a 'royal' marriage.
Finally, I highly doubt that the King and Queen would have wanted a British Princes as their daughter-in-law. Not only would she have had to convert to Catholicism, but it would have been politically undesirable due to the Gibraltar situation. After all, there was just another diplomatic strain over this very issue the other day. Besides, I doubt very much that the Spanish royals (and government) would want the kind of tabloid press attention that comes with being related to the Windsors.