ORIGINAL: adecoy95
personally my favorite method of approach in this was in sword of the stars 1/2. each race having unique propulsion methods made the way they are played hugely different and rich in replayability and depth.
Although I like DWU it is in my mind flawed in this regard. There is simply not enough variation in what races can discover full stop let alone their propulsion methods. Even if two races discovered the same tech they would not necessarily use the same method of implementing it, actually it's highly unlikely. It this I'm ignoring spying.
Just take a projectile weapon. Various races have a preference for this type of weapon and with 6 properties that can be changed there could all have slightly different versions. With a preference for this type of weapon other types (beams, etc) could be hidden until discovered (after much research and stealing).