This is something I've wondered about the past few days.
I understand that these colonial expeditions were, more than anything, business ventures. They required huge sums of capital from investors, and of course those investors expected high returns for the high risk.
So where was the profit expected to be generated? How would explorers "sell" their expedition to investors? What could/would they have pointed to and said "this is how we will make money"?
They went for gold. They stayed for trade.
Chapter one; Why did we go? In 1578, England's Queen Elizabeth granted colonization rights of North America to Humphrey Gilbert. He died in 1583 and they were split between his brother and half brother. The half brother, Sir Walter Raleigh, would gain the rights of non-Christian lands South of Newfoundland and North of Spanish Florida while the brother, Adrian Gilbert, would get similar rights to lands north of Newfoundland. They had to colonize by 1591, else they lost the rights.
Raleigh, who would coin the name Virginia as a tribute to the Queen, set out in an attempt at exploration and colonization in 1584. The main idea was exploration and after a rough Spanish and native encounter filled voyage, in 1585 they set up a colony at Roanoke, N.C. (then Virginia) with lands granted by local tribes through negotiations with a local native named Manteo. He and Wanchese had returned to England with an early part of the exploration expedition in 1584. This eliminated the language barrier as well as provided an authentic encounter with real Native Americans in London. Manteo would engage in the culture, Wanchese would become frustrated by it. Manteo certainly helped to provide more intrigue about what was to be found by Raleigh. They both returned in 1585 when the first Roanoke colony was established. Adding to this, a returning ship from the expedition had taken a Spanish galleon while on an exploration leg in the Caribbean. It alone provided enough bounty to have funded the entire mission, enticing the Queen to further pursue Raleigh's colonization agenda. The Roanoke colony would be abandoned in 1586 but they would soon return and attempt a more permanent civilian colony (which is the famed Lost Colony of Roanoke and source of the mystery of the first "Anglo-North American," Virginia Dare, who was Raleigh's granddaughter).
Rumors and stories of legends had been circulating. It was said (though disputed) that Juan Ponce de Leon entered Florida on a quest for the Fountain of Youth. A few years after Roanoke, in 1595, Raleigh would lead a military expedition to find Eldorado, the City of Gold, in South America. It would establish native ties in South America that would also fuel further colonization. The spanish, controlling Puerto Rico at the time, were likewise seeking the golden city and clashes between the two European powers (who were in the middle of a war with each other anyway) were common. Raleigh actually set up a command post in lands he had taken from Spanish forces. After returning to England, and for a few reasons, he greatly embellished his findings in the New World. He was imprisoned by King James, but would be released later and again launch an expedition to find Eldorado. On this expedition he was told by the King to avoid the Spanish, which he didn't, so upon returning to England he was again arrested. In 1618, by order of King James, the father of Anglo colonization was beheaded in London.
The resulting rumors (and actual Spanish ships full) of South American gold and silver mixed with the "ownership" of land in North America, a land full of these curious natives like Manteo and Wanchese, begged a serious question: how much gold was there? British investors were willing to find out.