Hi Hermoine,
I do not ascribe to the idea that older civilizations built pyramids in Egypt. However, it should be considered that, as you mention, mortuary enclosures built for the rulers afterlife cult were present in Egypt from the earliest of times. It's unclear on many levels whether the mortuary complexes found in upper Egypt were also present in lower Egypt, here we can say the unification of lower and upper Egypt brought together two different views of creation and afterlife. It took until the reign of Djoser (with the help of a Heliopoltian) to formulate a unified Mortuary complex incorporating the traditions and cult activity of upper and lower Egypt. In this process pyramids for the first time became an element of the royal mortuary complex design, though unproven the circumstantial evidence supports that pyramids are a direct evolution of the benben solar icon worshiped in Heliopolis.
The progression of stone materials used in the royal sphere of temples dates to the 1st dynasty, the use of names associated with the solar cult also begin towards the end of the 1st dynasty, and then this also is the time that warrior king names are replaced with unifying names praising the kings relation as unifier and God. The first Solar cult royal name arrives with Reneb (or Nebre) at the start of the 2nd dynasty.
Returning to the Great Pyramid, we cannot assume entirely it was always intended to be a pyramid, nor that Khufu was the first to build there. The site has many indications of early use during the predynastic period. If we examine the terrain we find the pyramid was built atop either a hillock or perhaps a butte similar to the many existing in the western desert. If we imagine, as that is all we are able to do, this elevated portion of the plateau had early importance to the afterlife cults, it makes sense that it may have held historical value and perhaps more importantly could very well have been the site of an early mortuary temple. If I had to choose that temples location at Giza it would be the 'Queen's Chamber', for here we find many adaptation results in the chambers stone composition and as well the same with the passage leading to the chamber. Moreover, the recently re-discovered Dixon relic (cedar from shaft) substantiates, in part, a much earlier date for the chamber. For example; the stone composition of the east and west walls of the chamber mirror each other with the exception of the Niche, though it is the Niche that determines the height of each course on all four walls, oddly the Niche is not centered on the east wall, additionally the top of the 6th course on both east and west walls was lowered 5-6 inches for some unknown reason. I suspect those two walls belong to a much earlier construct - a very early royal mortuary complex. In this line of thought it was not originally a burial site of a ruler but the cult center of the rulers afterlife much in the way the kings of upper Egypt built there own mortuary cult enclosures. Moreover, we have the archaeology discovery of G. Reisner in the north wadi which clearly indicating 3 different epochs of burial at Giza.
Again, pure speculation, if this were the case we must consider the influence early Heliopolis had at the site, and what impact that would have for future kings wanting to build there. As I have stated here many times I believe there were three different constructions built on the site... the last iteration by Khufu. I don't believe his body was interned in the pyramid, but that the pyramid contained sacrificial elements and bore representational sarcophagus of afterlife gods, nowhere in Egypt are Royals buried above the ground, the tomb is always below ground.
If we weigh the efforts of Sneferu, adopting pre-existing structures to build over them a smooth sided pyramid we begin to understand it's not entirely out of the question the same was done at Giza, specifically to the Great Pyramid (but I believe all three pyramids). Khufu's pyramid is so large because it has been built to incorporate a pre-existing structure that itself was built over an even earlier structure. This is why you have two sets of shafts in the building, why the apices of the QC align with the Great Step and the east-west centerline axis of the pyramid... and why the entrance (north side) of the pyramid is not centered on Khufu's pyramid.
All of these thoughts are more reasonable than the Orthodox view, which is the reason so many are unable to solve how the Egyptians managed to build something of such magnitude in 20 years, because it cant be done that's why. But, if it were the result of a common human endeavor, to incorporate a sacred older site, then we can see that half the volume of stone used was already in place, Khufu adapted, incorporated an older structure because of the historical content and value of the location. We see the same thing occurred at Saqqara, not only with the step pyramid and how it was enlarged but also that the 2nd dynasty tombs were built over and incorporated into the mortuary complex as well.
B.A.Hokom