There were a lot of similaraties between Quetzacoaltl, Viracocha, Osiris. This similarities doesn´t mean necessaraly that they have come from Europe. There a lot that we don´t Know for sure yet. The orthodox theories may not be right. There is a lot to discover and I only see discrepncies and incongruities in this theories. It give me the impression of that theories need studious a little more open minded.
By the way, Quetzacoaltl itá a astec god and Kukulcan it´s a maya god but they are only differents names for the same entity. Studies believe that He was a real person.
Date, a fruit produced by the egyptians also were found in south america mummies just like coca was found in egyptians mummies. I believe that when you put the language as a obstacle I do not agree because here we are talking about this great subject and the language here in Brazil is Portuguese. English and Portuguese are languages totally differents.
You said " For me, the give-away would be linguistics and writing. Certainly, if there were some transmission of building techniques from Egypt to Mesoamerica, there'd be loan-words from the "teachers" to the "students" (or vice versa) but I'm not aware of any. Also, given the logistics of building a temple or pyramid, it's surprising we don't see any Egyptian hieroglyphs which were so common in keeping track of such efforts by the great Project Managers of antiquity, like Imhotep. But again, we don't see any such like. Mayan and Aztec glyphs don't seem to have any corelation with any kind of Egyptian heiroglyphsl and the Inca quipu aren't related to anything, near as I can figure."
If a major cataclism or a very long Ice Age take place right now as we speak the computers will be destroied, books and documents will get ruined how the other cycle of civilization will know that we all had a major comunication system like the internet for instance?
The civilization had many cycles. We are only just one more, just like the mayan culture believed.
We really do not Know for sure what happened in the past a very ancient past.