A simple 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.
Start out by grabbing some spice geysers quickly (make sure your Vehicle's specialty is speed). 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 Merger superweapon to win the stage entirely.
To start, do as many missions as possible, aim for about 5 million Sporebucks. Buy 7-10 Colony Incredi-Paks, and colonize planets with a wide variety of spice, do not aim for just rare spices (though make sure to find them too, as they are also important). Use remaining money to buy terraforming tools to terraform the planets, build buildings, and buy out star systems. Many of your colonies should be powerhouses for spice, so you should run around your empire, continually picking up the spice produced by colonies, and selling them for high prices. Make sure to beam an animal or plant up right after you place it on a planet so it is needless to pick up more.
To get the most value from your spice, try to colonise planets with rare spices. The higher the rarity, the more money the spice is worth on the market. Don't sell your spices immediately when you go to the trade menu, find out what your spice is worth, and try to find a buyer who will buy at a high price. The price planets will buy spices from will vary over time, so if you find a buyer who buys at a good spice, collect all of that spice you can find and sell it there asap. The rarest, and therefor the most valuable spice, is the purple spice (not to be confused with the pink spice, second rarest). Finding and colonising planets with these spices will give you lots of profit.
Make sure that you build lots of buildings on your spice planets, as to get the fastest production of spices. The ideal setup, wich yields the highest production from a city without bringing sadness to citizens, yields 198.00/hour. Try to puzzle together that setup, and remember it well, and replicate it on all of your cities. Having more cities obviously increases production rate, but also storage space, so terraform your planets to T3 for maximum profit. Don't be afraid to invest in storage containers, as they will increase the amount of spice you can save on your planet.
A special, but complicated trick to getting as much profit as possible from a single planet, goes as follows:
1: Find a solar system with at least one planet with a very rare spice (try to look for the purple ones).
2: Terraform the planet with the rare spice to T3.
3: After stabilising the ecosystem, place down a monolith.
4: When whatever race evolves reaches the space stage, start a trade route with that planet. Alternatively, if you don't want to spend money, you could try to take over the planet, but this is very risky, because you might risk destroying some cities. This is the worst case scenario and should be avoided at all costs.
5: Buy out the solar system (skip if you took over by force).
6: Optimise your cities. This might be more difficult than usual, because the city layout of home planets is dissimilar to that of colonies. Try to get a good production rate for each city.
7: Place down a storage, and possibly every other colonisation tool you have (uber, eco, etc).
You now have a planet that produces the rarest spice at a very fast rate, and has anywhere between 50 and 100 storage capacity. Sell your spices at the highest price (for purple, any bid higher than 50k is good). Even at the lowest of 50k, this gives you a profit between 2.500.00 and 5.000.000 sporebucks.