So, all this time I and all the Spanish people I know have been busily mispronouncing manchego, mala, abrazos, tan, hacer, vamos, Madrid, etc?
I'm not sure how anyone could mis-pronounce those.
I studied the for 5 years, with Mexican, South American and Spanish instructors, and I never noticed a particular difference in pronunciation of basic vowel sounds. Certain combinations, perhaps, and there are several regional variations with consonants.
The thing is, no matter what the differences are from region to region... nobody's wrong. It's just different. And, instead of spending a lot of time blaming those bloody colonials for ruining the language, the Association of Spanish Language Academies has made a significant effort, over the past several years, to recognize and reconcile those variations into a comprehensive and inclusive "official" Spanish language.
So, as amusing as I find observations on the differences between British and American (and other regions') English, maybe it'd be more useful to follow that example?