As one of maybe four people on a 100+ team who really wanted to have the science nailed down, I had to recognize that I was fighting a losing battle. The artists and system designers (the guys who designed the weapons behavior, equipment, and general gameplay) would come to me with things they wanted to do, and my job was to try to find a way to rationalize it.
The primary means of getting a "truthy" feel was consistency. Something may be complete hokum, but if the hokum operates according to consistent rules, with reasonable drawbacks and limitations, and is logically exploited throughout the IP, people will buy into it.
The primary example is the mass effect. The unobtainium can be used increase or decrease the mass of a volume of spacetime. This explains not only the FTL drive, but artificial gravity, inertial compensation, projectile-repelling "shields," mass drivers with absurd accelerations, materials science (armor sheets are compressed to high density by "baking" in a high-mass field), architecture (impossible load-bearing), and tactics. Tanks can be dropped at high speed and soft land while the ship scurries clear of any ground fire. Soldiers can wear mass-decreasing backpacks to "super jump," and wield devices that project short-lived microsingularities.
My model was how Star Wars "feels" more realistic to me than Star Trek. Star Wars is just fantasy with chrome paint, but Star Trek, for all its technobabble, treated its tech base and its world so inconsistently and illogically it's impossible to believe in it for long. Matter-energy conversion is used to save transit time, play games, and make hot tea, but isn't used as a weapon or in construction. Sensors can scan for "lifeforms" from orbit, but can't detect a "cloaked" enemy a few kilometers away. When the ship gets hit aft, consoles on the bridge explode into sprays of rocks. Ships never run out of ammo and are always spotlessly clean - even after being "at sea" literally for years.
