I feel like trading produces only a paltry sum.
Perhaps the cash you make from trading should be linked not only to where the run originates and lands, but also to the identity of the traded good. Contraband producing cash mostly for the civvies, with different goods (say, alien artifacts?) producing cash weighted heavily to the government.
Remember that the things you do in your empire cost money-- look at that wealth tab to see where its going. Those construction factories you built all cost money to build, and then you've gotta fund them with money for every single thing they produce. My early game sees a huge yo yo effect-- I tend to go massively negative at the start while I gear up production and mining operations, then as population centers come online and a couple civ industry techs get developed, I go way positive.
It is at that time that I declare a world a financial center. Different people have different opinions on these worlds. Once financial centers are built, they can never be moved. This means any people running that center cannot be tasked with working in factories, so I segregate them from produciton worlds. I drop about 200 factories onto a planet, enough of the two resources to keep them running for years, and then set them with building endless centers.
A 250 m population tasking most of its industry to financial centers produces about as much in taxes as a billion citizens paying the standard rate. You don't notice a few financial centers much. The cost of producing them can even hurt when you're low on cash. But they will never stop giving you money, so having a lot of them brings a lot of permanent cash flow.
Thats a big help as your industry REALLY gets going (how else are we going to fund those 50 kton light cruisers?)