Considering that Spanish and Portuguese colonization effort lasted hundreds of years, the attitude changed significantly over time.

In the beginning, the nobility were very interested in exploration, not the least of which due to competition between "Spain" -- meaning the Kingdom of Castille -- and the Kingdom of Portugal. The negotiations leading to the Treaty of Tordesillas were done under the very dark shadow of Columbus' travels. So there was a lot of pressure at the top to advance their respective kingdom's interests.

Further, Columbus' early reports promised great riches, which of course attracted many adventurers who made their way even without any authorization from the crowns. However, it was accepted that the travel was very risky, and survival was nowhere near certain. This set the tone for the first part of Spanish (and Portuguese) exploration of the Americas. They were undertaken mostly by men, most of whom expected to return to Europe with their riches.

One of the early voyagers warned in 1544,

The ship is a narrow, tight, prison from which nobody can escape even though there are no bars or chains, and so merciless that it makes no distinction between its prisoners. The feeling of being crushed, and of suffocation and heat, is intense; bed is usually the floor, some bring pillows, ours were poor, small and hard, stuffed with dog's hair, and we had miserable goat's hair blankets. There is a lot of vomit in the ship, and a great deal of bad temper, which makes many people lose control completely, some for a longer time than others, and some unceasingly. The thirst you suffer is unbelievable, made worse by the food, which is biscuit and salted things. The drink is a litre of water a day, you have wine only if you bring it. There is an endless number of fleas that eat you alive, and clothes cannot be washed. The smell is awful, especially in the hold, though it is insufferable everywhere in the ship… These and other travails are quite normal in the ship, but we feel them particularly badly because it is not what we are used to.

Destinations also matter. The Rio de la Plata expeditions were known to be extremely hazardous, and explorers had a hard time finding any crewmen. In desperation, they lifted the ban on moriscos, jews, and muslims, yet still ‘despite everything, in the whole of Spain people could not be found to come’.

The state of being as one embarks on the journey, and contemplate return, also matter. ‘Those of us who live far out here’, an old and infirm settler wrote from Trujillo to his family in Spain, ‘live with no other wish than to end our days at home, in our country.’

However, returning to Spain is complicated for the poor, as ‘those who come out to this country cannot return to Castile without money, for everyone would laugh at them’.

Later on, as Castille's economy suffered in the 1600s, many write of home as having ‘so much misery and suffering that there is no future for anybody there’, such that they are determined to relocate permanently to New Spain.

Source: Kamen, Spain's Road to Empire.