Hence the English/French/Germans/Dutch never mixed with the other, while Spanish peasants mixed with Indian peasants (and Spanish nobles simply had no reason to mix with Indian nobles).
The English and French on the other hand, came to settle.
I think both of you have hit on parts of it (at least in my opinion). For the most part the spanish did not send women, just men to take the riches back to the country. And they interbred (and as Leauki said, the nobles did not do anything noble). And yes, the english, upon realizing they missed El Dorado, came to settle, so they brough families and saw no reason to intermix.
I have not studied the mindset of that period so do not really know if there was an aversion to intermingle (except for John Rolfe), or a more willingness to. Another thing to consider is that with the Spanish (and Portugese) came the missionaries and it was seen as a "god's mission" to convert the heathens. The English really were not into that at the time either.
Now one nation is not really represented, because of their loss of their lands. And that is France. But with very few exceptions (Montreal), the French came to tap the natural resources, not plunder for gold and silver. They lived well with the natives (and that was why they fought on the French side disproportionately during the wars before the revolution).
Since they were not here to settle, or convert, they fall into a 3rd category, but there is no real nation that reflects their heritage since all their colonies were taken over by the English (or later lost for other reasons).
Anyway, this is far afield of the topic. I just have always found the differences somewhat intriguing. And I suspect what Leauki said about Nobles may be a prime reason for the difference between the development of the english new world and the hispanic new world.