In DL/DA I would research up to the end of the Planetary Invasion tech branch so I could build transports with the ATM and invade high population planets with the mini-soldiers option.  The 500 BC was well worth it once my economy reach the point of a comfortable surplus, against developed >=10 PQ planets with a moderate or high population.  However, in TA a change was made that you lose any planetary improvements for which you don't have the technology.  Given the different tech trees in TA combined with the fact I play on suicide so the AI is usually further along in tech, I lose most of the planetary improvements.  Therefore, now I only need to research to Tidal Wave before I can start invading planets at a cost of only 200 BC with transports using the normal troop modules.

I wish this change was not made in TA as it would be cool to capture planets with different planetary improvements to your own.  I would say only unknown planetary improvements should be removed should from your build queue but already completed items should stay.  However, it would not make sense for organics to benefit from charging stalks or the Yor from farms but isn't that already possible with tech trading/stealing or were these tech excluded?

It is not possible to decommission unwanted super projects or capitals but can't a Tidal Wave invasion wash that away?