The techs with a star are unique to that race in the sense that they are the only one able to research it. Once you acquire it through trading, you get the usual benefits from that technology.

Especially the minors are perfect to sell techs to early on in the game, as that can help your economy to stay afloat. The added benefits are that it causes the minors to develop faster; in particular technologies that give them access to tech / econ / manufacturing capitals are interesting if you're planning on taking over their planet later in the game

With regards to the other AIs you need to be a little more careful that you don't give them too much of an advantage. In any case (minors or other AIs) never sell them techs that grant a bonus to diplomacy since that will make future negotiations less fruitful.

The whole trade thing is a balance but generally speaking the AI tends to value quite a few technologies rather high, which leads to the "2 or 3 to 1" scenario you encountered. Don't forget you can also add up to 999 influence points to help make a deal. The whole balance strongly depends on your versus their diplomatic ability (see also the comment in the middle of the screen when youre trying to make a deal - this will indicate who has the diplomatic advantage)

After one year, you can easily get economic and research treaties from the minors in return for a few more advanced technologies. Some that I love are population growth techs and less advanced weapon techs, especially if the minors already researched another weapon branch there's little reason not to give them access to some basic stuff they won't use anyway but pay good money for.

A great thanks to both of you.  I have been making a good little chunk of money selling off stuff to the minors, and I have limited what I've swapped with the major's outside of the couple that seem to be friendly at this point.  I figured giving them anything to do militarily wasn't a good manuever, but I had thought about the boost of getting them some Econ stuff.  LTJim, I remember, from that other post, what you said, in this particular game it's to late for that, but I have a feeling I'm going to start another game here in the next day or so and I will put your flagship upgrade gambit into the game and see how well I can manage.  Thanks for the info, it's greatly appreciated.

PS - Noctilucus, I'm playing the Terrans, so I obviously don't have access to a description of the other races "special" techs, any idea where I can get a description of them? 

I think you meant the mining ship upgrade, not the flagship.

One day, I will play a game with essentially NO habitable planets and use space mining but on all other settings, space mining is just not worth the trouble.  I used to delay the mining ship conversion to a colony ship until after developing the asteroid belt right at the home system, but even that seemed not worth the delay in that second colony.

Remember that you will get incrementally more in each Minor AI trade if you have better diplomacy levels.  Thus, it is a reason to grab/build the Translator trade good along the way, as well as another reason to work one's way up the government path.