I like the idea of the first country to reach a new technology gaining some additional benefit from doing so.
A general problem with tech trees is that the player wants to gain some advantage through research, but many times the player is able to get so far ahead that the game is decided (the classic tanks vs. mongol cavalry in civilization). How can this be avoided without taking away all of the advantages of research?
One way is to give advantages to the first player to reach the new technology. That's an incentive to research. But in the same vein, it could also become easier for others to research that technology because it's out in the world now and it's always easier to copy than to innovate. Perhaps the technology becomes easier and easier to research the longer it has been out in the world. That would help prevent having some countries with space ships while others are still using cavalry. The first person who got gunpowder will always have better guns than everyone else, but it's a lot easier for other people to make guns once there are working examples out there to be copied.
There could also be bonuses to research gained when conquering cities. For example, if you conquer a city from a country with a number of technologies that you don't have, you could get research bonuses related to those technologies. Say the city has a farm and you haven't researched farms yet. It stands to reason that it would be easier to research them if you've got a working sample.
I don't think technologies should ever be given away, though, even in trade between countries. THere's a world of difference between knowing how to build something and having the infrastructure to build something. I think part of the research process is developing the human and physical capital to actually implement the idea. Farms, say. It's not just knowing that plows exist. It's having enough smiths who know how to make them and have access to enough metal, coke, etcetera to do so, and then have them distributed to the farms, and then teach the farmers how to use them, not to mention getting livestock to do the pulling.