The original idea of imperialism and colonialism was that additional provinces/colonies equal greater wealth.
This has always been quite questionable because that wealth is difficult to transport and a mere illusion if it's far away. The transportation costs were prohibitive for long-distance transportation of everyday goods right up to the 18th century.
The Roman profits off controlling England were mostly restricted to a flow of metals. This flow was probably beneficial for the emperor, but not for free; wealthy men living in England were most likely getting paid for it. The empire had on the other hand to maintain and mobilise armies in order to fend off the Celtic neighbours.
Another example is the Spanish experience in the New World.The initial costs were small and a lot of gold and silver booty was carried home. That was the raiding part; the colonialism looked different.
Few New World goods other than silver were really valuable enough for transportation to Europe. Soon, the balance of colonialism for Spain looked like
* loss of enterprising men, ships, crews, ruler's attention to Europe
* gain of silver shipments
The silver had little intrinsic value. It was important for money (coins), cutlery, dinnerware and mirrors mostly. Spain was able to import wares from other European countries and to pay foreign mercenaries with its silver coins.
The net European wealth gain from Spanish colonialism was probably close to zero, though: More silver did not mean more wealth because it's really just money.
Money has the illusion (and ruler -or state-given guarantee) of being useful as payment for natural goods. The reason for its existence is in part the fact that it's easier to transport money than goods. More money in itself doesn't mean more wealth to a nation or continent; the larger quantity of money is still used for the same role - all payments. The more silver was transported to Europe, the lesser its purchasing power because an ever larger quantity of silver was used for a quite stagnant real goods trade. The amount of wares (and mercenaries, artists) that Spain could import from other European countries every year with its colonial silver dropped year by year.
Spain took severe economic damage in the 16th century because of a neglect of domestic economic development and reforms. It turned out to be a rather mediocre country in the 17th century. The control of most of South America and Central America did not turn Spain into a truly prosperous country.
Spain kept importing mostly silver from its colonies; the few other volume imports were paid for with equal volume of exports. Silver = money = illusion. One could say that colonialism was at that time only about the import of illusions and luxury goods such as sugar.
Maritime trade did intensify later on (especially since the early 19th century) and more goods were traded between homeland and colonies. Repeat; traded. The Europeans who emigrated into colonies did expect proper payment with European goods for their work. The end result was from a European perspective an intensified trade. There were few advantages to Europeans from exploitation of indigenous people because those advantages were largely soaked up by the colonists.
In the end, colonialism and imperialism were stupid. The classical Greeks and the Portuguese were right with their approach of colonies in form of emigrant trading cities and trading posts.
It's interesting with this in mind when one looks at all the wars that were waged over colonial "interests" during the 16th to 19th centuries.
The great irony of all this is of course that imperialism and colonialism became politically unsustainable at the time when the transport of low value goods had finally become affordable!
P.S.: I wrote this years ago, decided to release it with minor tweaks after all instead of having it wasted in the non-public list of drafts.