Timothy.lucas.jaeger 15:58, 21 July 2008 (UTC)
I did some testing on upgrades of planetary improvements in Dark Avatar a while back, not sure which version. A tile's first upgrade works like dog of justice describes. For subsequent upgrades, the discount is equal to the cost paid for the previous upgrade. Suppose a basic factory is built for 50, then upgraded to a (standard) factory which has a total cost of 75. This is the first upgrade so the cost paid is 25. This 25 is the discount for the next upgrade. Say the next upgrade is to an enhanced factory (total cost 100). The upgrade cost is 75 (100 minus 25). For a final upgrade to industrial sector with total cost 400, the buyer pays 325 (400 minus 75). If you do the math, you find that the total cost of the tile is the sum of the costs of the final improvement and every other improvement before. In this example the total cost is the industrial sector plus standard factory (400+75) = 325 + 75 + 25 +50. It doesn't affect the calculation if the upgrade is to a different type of building, e.g. factory could upgrade to research lab or farm etc.. Afaik, the only benefit of decommissioning versus upgrading is to avoid maintenance costs.
Iztok (Oct. 2016)
I can confirm that. In my recent game (1.53 DA) I'm playing all-factories and did upgrade captured Research Academies with Trade centers (very cheap upgrade). Now I'm upgrading Trade Centers to Banks and on many planets paying almost full price.