I have read through this thread, looked at all the suggestions, and come up with a few of my own. One of the big problems I am seeing people have is how with the new unique techs for each race, It will all basically stop being unique the moment the tech trading gets going, or the invasions begin. And with the AI doing it, If people dont follow suit, they will quickly be at a disadvantage, so even if you choose to role play, the AI wont.
One solution I think would work for this is a possible reverse-engineering ability. Capturing or trading for a better version of farming or manufacturing from another race, instead of giving you that building, can open up another tech line that you can put researche into that will integrate some of the bonuses from the better tech into your own races buildings, like the drengins in the original post. Instead of the farms with the passive growth bonuses being overwritten, they are given bonuses based on the racial tech that was captured. And to keep them from suddenly having overpowered farms everywhere, the original farms overwritten are prototypes requiring both research and manufacturing put into them to make them finish up and available to the rest of your empire.
In the case of a traded tech, you can designate one of your worlds to be the place where the prototypes are first built. This would also add a strategic element to the game as well, defend the planet where they are being built and tested. I dont know if this idea could be implemented before the scheduled release date though. Also, this gives rise to the possibility of an Uber Farm eventually being made, so it might be wise to exponentially increase the cost of integrating additional technologies into the same upgrade type such as farms, manufacturing centers, research labs, and commerce centers to reduce the likelyhood of the uber empire of doom popping up.
It would also force you to choose which techs you would want to integrate first. Maybe also make it possible to do more than one integration at a time at an increased cost to your empires reasearch and economy. Essentially this method would be siphoning research away from your main research branch into the integration process, so while you would still be researching those Death Rays or Terror Stars, the progress would be slowed depending on what reverse-engineering you have going on.
Hey, it sounds kind of like a Super Project, except on a bigger scale... That might work, turn the whole process I just described into a Super Project that doesnt just build off of planetary resources, but resources from your whole empire. If you Capture a tech or trade a tech that is unique, a Super project can become available to integrate that tech into your exhisting buildings, giving you access to a better model with enhanced bonuses, with the stipulation that a captured tech must have its project build on the world that it was captured on, giving a further tactical consideration when invading. The need to defend a captured world that it is being built on, and assign a higher priority to the ai for recapturing said world in order to prevent its enemy from gaining access to that tech. Wow, that sounds complicated now that I think about it. Well, this all may just be a monumentally stupid idea, but I think it could work. Heh, this has all been just one big ramble, but hope it inspires someone...