In general, as the other answer indicates, colonization made the colonizers wealthier, often vastly so, and usually made the colonizing country stronger, at least temporarily, because of the wealth flowing into its coffers. Great Britain was able to use its colonial wealth relatively wisely for many years, maintaining superpower status, while Spain quickly squandered wealth garnered from early colonies in the Americas.
Nevertheless, as more than one writer has outlined, colonization could also have a debilitating effect on the colonizers. Greater military might or simply a sense of cultural superiority often led to colonizers holding the native population in contempt. Therefore, colonizers sometimes missed valuable information or wisdom from the indigenous population that could have helped them survive. As Jared Diamond points out in his book Collapse, for example, the Scandinavians who colonized Greenland could have survived had they been willing to adapt to the Native American ways, such as by learning to fish in kayaks, but they persisted in unsustainable European versions of agriculture.
Writers like George Orwell also illustrate colonialism's ill effects. He describes how harmful British colonization was to the colonizers in Burma, who got locked into an irrational system of domination that led to decisions based more on saving face than having any concrete value.
In other words, colonization came with a price. Conrad's fictionalized account of colonial intrusions into Africa in his Heart of Darkness is just one of many accounts of the shattering effects of colonization on an individual.