Also to add about trade routes. Races should be able to trade within their own empire. If players play on smaller galaxy sizes and few races they miss out on the extra potential income from trading. Move a freighter into one of your planets, special button "Create trade route" select destination planet.
I don't see the point of this at all. You're just moving money from Planet A to Planet B - you know overall how much money your race has, so there's no increase to the overall treasury.
Trade certainly needs to be made a more attractive option than it is right now.
You should get credits based on your relationships with other races/what those other races want. ie you sell to the Torians, they are Nuetral so your stuff's worth 10bc per freighter, the Alterians who you're verging on Close to will pay 15bc per freighter. Now, you might go with selling more to the Alterians but you know the Torians have more "things" to offer diplomacy-wise so it's not just a case of who's offering more cash right now but who can help you in the longer term? Trade and Diplomacy working together.
The Treasure Hunt - Pirates should be able to hijack these so you may have just spent that 250bc (or whatever the cost of it is) and, yep, treasure was found but those big men with guns were very persuasive and sorry, we gave it to them...
Agree with Triple Crown about the order of the three ways you can get money being wrong, except I'd go Trade/Building/Treasure Hunt.