Someone suggested on page one that you could only trade techs you yourself can research.
Good luck. I barked up that tree non-stop leading up to TOTA and it never went anywhere. Tech brokering is a good start, but for those of us who want truely unique races, that was really the only option I foresaw working the best. And I STILL believe that.
First of all, the research tree describes the potential knowledge of your civilization. This means that due to some sort of unique circumstances, your race can understand certain concepts that other races cannot. After all, are you telling me that I can design a gun that fires BLACK HOLES, but not a way to make my planets more fertile and healthy? Obviously something about that technology is dependent on a very special set of circumstances that exist ONLY to the Altarians and the Drath.
Here's an in-game comparison - the Thalans. All the Thalan history is based off of Gravitrons and Temporal Mechanics. You cannot trade these technologies to anyone. The reason is explained in the lore - the technology is all based off understanding a fundamental particle of nature that nobody else knows exists (Gravitrons) that exists in dimensions nobody else can comprehend (11 of them). It's IMPOSSIBLE for another race to understand.
If you want an idea of what this is like, I want you to think about how you'd explain what the color 'red' looks like to someone who has been blind since birth.
The fact is, for lore reasons, most races have no business trading semi-unique technologies. The Drengin and the Korath, being Drengi, have unique physiology that allows them to sense and derive pleasure from pain other creatures feel. No other race can do this. Therefore, exactly WHAT USE would Terrans have for Pain Amplifiers? Go ahead and puzzle THAT one out for me.
This would also fix exploitable behavior. Torians are supposed to be poor researchers, hence their weak +Research% bonuses. Have you ever seen what happens when the Torians trade for DISCOVERY SPHERES? They go from the WORST researchers to the most brilliant minds in the galaxy.
Not only would this provide a very SANE and PRACTICAL set of limitations around the completely-broken tech-trading system, but this would also:
- Encourage trading amongst 'similar' races - Altarians and Drath, Drengi and Korath, for example.
- Curb the obscene 'everything must go' behavior of the AIs.
- If you're worried about this crippling your races, think again - probably 80%+ of ALL tech trees share most of the same technologies - miniaturization, weapons, defenses, hulls, diplomacy, etc.
Seriously, throw me a bone here. I couldn't POSSIBLY make a better case, so I don't see why this keeps getting swept under the rug. Hell I don't even see how this would be difficult - you wouldn't have to revise the tech tree .xml files with new flags - conceivably, nothing more than an 'If - Then - Else' would work.