It depends on who you ask. The people who were discovered or those who sent the explores.
Most of those civilizations that were discovered ended up part of one king's or another's domain. There were very few that saw real economic gain from being discovered.
The explorers also spread diseases both to and from the new civilizations encountered. Although, with as many plagues rampant in Europe between the 13th and 18th centuries and poor record keeping; it is hard to estimate how many people died of new diseases brought home by explorers.
Those people who sent the explorers gained more from the discoveries made. New sources of riches. Especially the biggest source of wealth, land.
