I propose that their be branches of tecnology devoted to the Reserching of OTHER race. (This is completly independent of have special tecnologies that only a particular race can reserch).
Many of these tecnologies would be things that Moo2 generalized among all races for example the DOOM virus. How can this 1 virus affect all races, that seems highly flexible, it can even work on races you didnt even know about when you invented it??
Instead we would have a branch of the tec tree that can not be reserched untill you make contact with another race and which provides you with bonuses that get aplied to interactions ONLY with that race.
So you can Reserch the Alkari Doom Virus to kill alkari's with, or Reserch Klakon Culture to get +3 levels of Diplomacy with the Klackons. Or Basic Psilon Battle tactics to give your ships +10 combat power when they fight the Psilons. We can think up all kinds of cool tecnologies that fall under this heading, they just need to have the following in common
One of the prerequisites for reserch is contact of some particular type (like you have to be conducting trade before you can conduct the "basic Klackon Trade Negotionations reserch or you must have battled the Psilons to reserch "Basic Psilon Battle tactics")
The tecnology grants a benifit when interacting ONLY with the targeted race. The Klakon Doom Virus kills only Klackons, understanding Psilon battle tacktics only helps me fight the Psilons.
The tecnologies could start off with the basics like "Psilon Autopsy" then "Live Psilon Behavior" then "Psilon Language" and "Basic Psilon Culture". These tecnologies act as keys to unlock further reserch options and most importantly incresse your diplomatic options with the particular race (Cant sign a treety if I dont know their language)
And because these tecnologies can be trade just like any other tecnology it greatly incresses the importance of the ENEMY OF MY ENEMY IS MY FRIEND because he will most likly share these valuable tecnologies with you if you agree to join in a war aliance against his oponent, especialy cause you cant stab him in the back with the tecnologies at a latter date.