rofl i trade because at some point it just becomes exponential. if you manage to get trade goods, and have a good position between a few races, you can make so much bloody cash with trade it's not even funny. In my massive game I'm playing now, i've lowered taxes by 20% because still made 700bc/turn in profits, and I spend about a fifth of my revenue on military. with the profits, i simply hurry construction when i can.
Trading with a couple races(the ones most compatible with you) can be quite useful. and then, once you took out those who oppose you, turn on them and crush them by barely stretching your hand over their territory
at that point citizens wouldn't care about u heightening taxes, if you play it smart, they'll love you, (i have 96% approval at a 45% tax rate) And choosing good, then just annihilating everyone also works to give you bonuses in the social and defense aspects.
I kinda act as a Judiciar, one who'll force good on the galaxy simply by wiping out all evil races, while converting neutral ones and forcing other good races to surrender to you.
It's surprisingly efficient