Making money

WARNING: SPOILER. READ AT YOUR OWN RISK
Personally, the easiest way to make quick and easy Sporebucks are by getting the blue traits (Omnivore, Adaptable, Industrious and Economic. This will lead to the Space trait Trader and will get you the ability of Cash Infusion which greatly helps in buying out star systems.

Civilization Stage
Start out by grabbing some spice geysers quickly (make sure your Vehicle's specialty is SPEED). I'd say 2-4 is a reasonable hit. If you have time, raid a few tribes for more vehicles and money. By now, a tribe has evolved into a civilization. Get your relation from 0-100 and propose a trade route with that city using several vehicles. Try to keep dominance of all the spice geysers on your continent. If you are a sea city, claim some offshore spice-rigs.

Soon, more nations will appear. Economically, you should be able to out-perform them by adding buildings to your city and claiming more and more Spice Geysers. Keep your relations up with the empires closest to yours and slowly buy out five cities in all (you can choose to blow up/convert one or two) with your trade. Once you have the airplane, you just won the game. You now can open up trade with the entire world. Be careful not to get in bad spots and when you get the money (and six cities) use the Global Buyout superweapon to win the game entirely.