On diseases affecting the Guanche, why so? the only disease that could possibly be of great impact would be the plague which isn't until the middle ages. I'd imagine given how old small pox is and the genetic links between the berbers and the gaunche peoples they'd have been exposed to smallpox at some point long before the era to which I refer (600-650AD and beyond).
I gave the inland empires as examples of my theory, though i agree with you. We could also see a situation where the coastal kingdoms that develop expand militarily inland and the technology has alternate routes to spread.
A significant amount of Guanche died of influenza, smallpox, and other diseases they had little immunity to, although being involved in conflict with the Spanish probably didn't help the disease environment. The reason being is they had been isolated from the mainland for too long