And the second improvement I pasted is the new building, the upgrade that should be available after researching the tech XenoManufacturingMethods. It isn't the InternalName of the tech, but the GenericName, in order to make the building available to all factions.
Yep you'r right .
As for preclusions, you shouldnt need any for the durantium refinery, its a colony unique so no need to preclude itself and the MegaDurantiumRefinery is an upgrade
so precluding it does'nt make sense.
You should add an preclusion to the MegaDurantiumRefinery for the durantium refinery,
else you would be able to build another one after upgrading it.
As for the MegaDurantiumRefinery showing up greyed out, this seems to be a problem with the Durantium cost,
if you comment it out it works like it should, so its most likely a problem with the game.