Alright! Something up my alley. For reference, I'm writing my senior thesis on Spanish empire building in Italy and going to grad school for British Imperial economic history. I'll try to put some books down at the end for reference, though most of this comes from classes I've taken over the past couple years. Also, I apologize for the relative superficiality of what is to come. I could go way more in depth, but that would end up being even longer.
In short, Capitalism is what separated the two pairs of empires. In long, well, let's get to it!
The method of Spanish and Portuguese imperialism was purely exploitative and short term. Let's first take the Spanish. They discovered two huge silver mines in the New World. The upshot of this? Think of Saudi Arabia, except instead of having to put their oil on the market and all the economic hurdles and structures that imposes, the Spanish just had a well of money. Using Native slave labor (the mita) they mined the everliving hell out of these places. Check out Potosi, a mountain with so much silver, that by the time the Spanish bled it dry, it had lost several hundred meters of elevation. In addition to this, remember that the Spanish discovery of the New World was one of the events that started the transition from the Middle Ages to the Early Modern Period. So you've got a relatively primitive civilization, at least in terms of economic understanding, with a seemingly unlimited money supply. The Spanish Monarchy is also constantly at war during this time. The idea of investment or any such thing (which we'll get into under the British and Dutch later on) was totally alien to them, especially at a time when there were massive and perpetual war expenditures. They had a practical monopoly on the New World from 1492 until the 17th century, so there were no exogenous constraints on their empire that would induce capitalism or a refining of economic policy. Simply put, they had fiscal needs and a wellspring of cash, so they just kept mining.
Due to the wealth of Potosi, it soon become one of the largest towns in the world. Yeah, that's right. This Bolivian backwater was, at one time, home to perhaps the third largest urban population anywhere on earth with around 250,000 people. However, this is exemplary of Spanish policy. There was no effort to develop an infrastructure or a varied economy or anything of the sort. The Spanish presence in the New World was purely exploitative and produced only pure cash. Now this could have been hugely beneficial, except the Spanish had already undertaken massive debts to German and Genoese financiers throughout the 16th Century. These grew exponentially after 1550 from 1 million ducats, to 7 million in 1556, to around 30 million ducats in 1600. Many of the loans the crown took out were short term with quite high interest rates. 20% was not uncommon and rates as high as 50% were often seen after the crown's multiple bankruptcies under Philip II (r. 1556-1598). The Spanish simply didn't create a structure capable of sustaining long term growth or economic health. The capital they gleaned from the New World immediately went into the pockets of the Germans, Genoese, and other floaters of their loans (these even included Dutch rebels and English nobility who were at war with the Spanish. Remember at such primitive economic times, the idea of extending war to trade or finance didn't occur to them) or into the pockets of Spanish nobility. There was next to no investment into Spanish infrastructure or domestic industry. Indeed, all the silver trade accomplished in Spain was a steep inflation that impoverished the Spanish lower classes. Outside of Spain, however, this silver provided a massive quantity of liquid capital that helped to grease the wheels of a globalizing economy. It's estimated that 60% of all silver that exists today was mined by the Spanish.
The Portuguese were similar in their lack of investment. To sponsor their missions to the East they went to the nobility to collectively raise funds for the voyage, and when the voyage came back they quickly divvied up the profit and that was that. Additionally, the profit, in the hands of the nobility, was largely spent on luxury goods like jewelry and art. You want an example of economically unproductive assets? There you go. They also had a very small population that could simply not support the massive territorial empire they expected to monopolize. Really the only reason they were able to seize the land they did was through their military superiority, bred on the battlefields and seas of Europe where anyone who couldn't keep up was toast.
The English and Dutch primarily got over this by way of the company system. The Dutch East India Company (VOC) was the first modern company (joint-stock company). They sold shares of the company which paid dividends at the end of each successful voyage. Revolutionarily, the profits weren't immediately and totally distributed to the stockholders, and people were expected to wait potentially 10 years before fully recouping their investment. This marks a considerable trust in the system by the Dutch people. This had two major advantages over the Portuguese system. First, the profits were able to be reinvested in future voyages enabling an entire enterprise to spring up. Second, they were able to raise a whole helluvalot of money through opening it up to the entire Dutch population. The Dutch at this time were, per capita, the richest population on earth so opening the stocks up to the common people attracted a massive and unparalleled amount of capital.
Once in the Indies, the Dutch didn't simply buy spices like their Portuguese predecessors. Oooh no. They monopolized the hell out of the industry. The Spice Islands are a tiny smattering of islands in the Indian Ocean where cinnamon and pepper trees grow. What had been happening is that, through a primitive system of trade, Spice Islanders just picked up fallen cinnamon bark and traded it with local merchants (as an example, "spices" included cinnamon, cloves, pepper, nutmeg, etc). The Dutch brought capitalism to the process. They enslaved or exterminated the Spice Islanders (the early days of capitalism show you what truly laissez faire capitalism looks like), set up plantations, and carefully regulated the spice trade. While the Portuguese relied on selling spices as a luxury item, the Dutch made it a staple for everyone. Spices saw a drop in value of around 90% under the Dutch, but it didn't matter, because there was so much spice on the market, all controlled by the Dutch, that they still profited handsomely. In fact, when the Dutch had too big of a harvest of say, cloves, they would burn much of the crop to raise the prices to the optimal level. These guys had discovered economics.
The British acted in similar fashion. I'll wrap this up quickly since this is becoming a novel, but they basically exploited the fact that they were an island and through a series of wars and legislation (see The Anglo-Dutch Wars and Navigation Acts), they picked up Dutch market share of European Oceanic trade. Such acts were simultaneous to Louis XIV repeatedly invading the small Netherlands which totally hamstrung them. Meanwhile the English picked up the slack. Additionally, their American colonies were highly productive. Unlike the Spanish, they created highly productive centers of mercantile and industrial output. In the Caribbean, they had vast sugar/rum/molasses plantations. Meanwhile the Thirteen Colonies, the richest colonial center possibly in history, were not rich from crazy and easily accessible natural resources, like Potosi, but from the human capital nurtured there. Shipwrights, fishing, lumber, tobacco, and a vibrant market economy created a huge amount of wealth.
I really should stop here, I'm sorry if I skipped over some important parts, please ask questions and I'll see what I can do to answer them.
To recommend one book, I'd say A Splendid Exchange, by Bernstein. It's fantastically written, and goes into detail about this.
There's a bunch of other books I could recommend, such as the Cambridge Economic History of Europe vol IV and Pomeranz's The Great Divergence
Similarly to what /u/kosherkowboy mentioned, I always thought Potosi was really more of a ruin for them than a blessing. While all of what he mentions is true, as far as them bleeding Potosi dry and spending on constant war, my understanding was that aside from all of the aforementioned, the Spanish were just terrible at managing money in the first place. Along with being known for their Armada,the Inquisition, etc, they were very very lavish. They spent so much on court and finery that coupled with the other spending they did, they did themselves in before they could properly benefit from their spoils. The book The Veins of Latin America Eduardo Galeano or *Latino Politics * by Lisa Garcia Bedolla properly explain the issue with Potosi.
How did the first two benefit more than the others? American gold allowed Spain to become one of the wealthiest states in the world, and Brazil allowed the Portuguese government to function in light of Napoleon's occupation.
Could you provide some context or examples?