Spanish suffered a phonetic evolution during the Renaissance era, adopting certain traits attributed by some scholars to basque language (partial lost of "f", no distinction between "b" and "v" (betacism), shift from "j" to "kh", five vowels system...The reasons? Mmm, repopulation, high influx of basque clergy and civil workers (the most literated people and best knowing of spanish language, despite not being in most cases their natural language!!!!)
Pff, the puzzle is desperating...
Yes it is, but if it wasn't we wouldn't have all this fun here, hehe.
I don't think few clergy and civil workers can make a difference how language sounds. It might be the case that records of spoken language in spain are misleading. What I mean is that most records, from the past, of spoken language are from big cities where. This is the language of educated elite, which in spain case, was influenced a lot by germanic speaking tribes invading in middle ages. Mind that way back 90% people lived in villages. But the records how spanish was pronounced there are not existant.
Previous differences in f, v,b, j, might be of germanic way to speak spanish.
Consider a scenario that after renaissance there was faster city growth mostly caused by influx of villagers. If this is a fast process you will see quick shift how the spanish sounds, getting more similarities with village version, which was probably closer to Basque pronunciation.
You can compare it to Latin (educated elite) versus Vulgar Latin for the villagers and the rest. The question is how come the elite and priests couldn't teach plebs the proper Latin? In this case one thing is obvious that few, even educated people, cannot change the way a language is pronounced by many. And we are talking about the ongoing process for few hundred years. That's why I don't see how few Basque intellectualists could change spanish language. It is more of a case of official spanish version in cities were influenced more by latin and germanic. Possibly arab invasion helped "cleaning" elite speaking version of spanish?
Here is a nice explanation about loss of sounds. What happens if english is imposed on Italians or French speakers? The sound H is dropped immediately, especially at the beginning of a word.
The sound shifts, the sound laws need big events to happen. People don't drop sounds or change them just because. Usually the big event is when two different languages are imposed on population, after invasion or migration for example. Make native Italians, Chinese, Indians, etc speak english and you will immediately see their local sound laws in action.