What is the one big thing that has been overlooked with spacetime curvature?

The curvature is in time also. That means that for Mercury to advance through the perihelion it needs to either follow a shorter path through the gravity well caused by the sun. Or it must spend more time in the orbit due to the curvature of space allowing the sun to advance the orbit.

That is highly significant because if time is affected then the local gravity of Mercury would be marginally less while in the gravity well. This has significance to the alignment in 2012 because the whole solar system may be going to go through a similar gravity well brought about by the Milky Way being in a super cluster of galaxies. It would be a brief window of reduced gravity but with no reduction in propulsion. It means even the most despotic tin pot country in the world could make a grab for the moon if it was prepared to organize for it.

The real goal would be Mars with usable soil and 0.8% atmosphere already. Even the payloads would increase from tens to perhaps thousands of tonnes meaning the CO2 and excess water could be taken to the red planet. It isn't as it there is not enough plastic to hold it, the pacific ocean is full of decades of accumulated waste plastic.

Sure there would be extra tectonic activity but the people would also be correspondingly more able to escape provided they kept up their fitness and calcium intake for bone density. Instead of the doom and gloom of the end of the Mayan cycle the world through not recognizing its significant might be throwing away the greatest opportunity in thousands of years. What other explanation could there be for building a Babel Tower that held such a short time and yet remained in the memory of humanity for so many millenia?

It is worth thinking about and should start to be very apparent within a year or two, cheers.

Michael.