I must preface my answer by saying that my own readings are mostly about 15th and 16th century Portuguese, and only partly go into 17th century, and even less into colonial Brazil. However the works about Portuguese Orders, on which I am sourcing my answer, often lump the entire early modern period together, where despite considerable changes the system seems to had remained constant and similar enough. To put the gist of the answer at the start, membership in the Orders was a highly desirable position as it was a window for social mobility and advancement, as well as providing direct and indirect financial gains.

Let's analyze the two main aspects of the membership: financial and social

 

Financial benefits

First it is important to note that performing services to the Crown and getting reward for it seems to had been the normal way of how Portuguese crown operated and incentivized members of their society to work for Crown's interests. It was actually institutionalized back in the middle ages, through two endowments given by the King to nobles and distinguished persona: the the tença and the contia.

According to the work State finance, war and redistribution in Portugal, 1249-1527, contia was

was a flat payment that allowed a king's vassal to maintain a warhorse as well as acquire good defensive and offensive equipment.

while tencia, for us the more important of the two:

stands for permanent revenues granted by the king in exchange for a service, already performed or to be performed. Indeed, the fundamental rationale of the tença was to reward services. and In the reign of Dinis, tenças were disconnected from the exercise of authority and, although occasionally allocated in specific municipalities, they were royal revenues collected by the royal administration that were temporarily diverted to a holder. They were, in sum, a rent. Unlike previous redistributive payments, it did not entail any function or exercise of jurisdiction, but merely the usufruct of the monies produced.

So when you see a Portuguese men asking for a reward for a service he provided, you are basically witnessing an application for an age-old system of financial compensation, in the form expected by all members of the society. Not all applications will be accepted of course, but denying a reasonable request would be scandalous.

Where do the Orders fit in here? By the end of Reconquista Military Orders of Portugal (Order of Christ, Santiago, Avis, Hospitallers) were the largest land holders behind the Crown (and maybe the Church), holding vast estates on former frontiers, shown in this map.

Since at least the 15th century Portguese Kings were slowly succeeding in bringing this Orders under direct Royal control, a process which finished in 16th century with the King becoming the automatic Grand-Master of all the Orders upon ascension to the throne. This brought all the Orders lands, incomes and resources under Royal control, and gave the King an option to hand out lands and positions and payments from them as rewards for services.

The orders themselves were hierarchical and different levels of members would be given different rewards. The highest nobility would get rule of commendaries, basically land fiefs. One person could hold one or more commanderies. The number of commanderies is estimated by Fernadna Olviera at:

The Order of Christ accounted for around 450, the Order of Avis for 48, and the Order of Santiago for 85.

The size of them varied, so Order of Christ's commanderies were more numerous but also smaller then the rest.

Lesser members would get either various positions or posts at this commanderies, or just payments of the above mention tenças. It is unclear if the tença was an automatic upon entry, but the records show the majority, if not all members would have this income.

So, without doubt, yes, membership to an Order was a major financial boon, giving you a steady income or even better, a nice cushy job for the rest of your life.

 

Social benefits

While financial aspect was important, the Orders allowed considerable social mobility in otherwise rigid and traditional Portuguese society.

For example, there is currently an ongoing debate on the level of racism in the Portuguese society of the time, on which I wouldn't really delve into at this moment, but which figures here so I must succinctly touch it.

Basically, in one hand, there was considerable amount of inter-mixing and inter-marriage between Portuguese general population and people of Jewish, Moorish, African, Asian and American ancestry, in mainland Portugal and especially colonies. On the other hand, there was systematic effort by the power structures to prevent people of such origins to achieve equal standing as their pure Portuguese counterparts. The opportunities to hold offices, positions in church, army, and institutions would be constantly denied to people with even traces of non-european or non-christion ancestry. Even creole whites were somewhat excluded, although to a lesser effect then people suspected of having so called New Christian ancestry.This culminated with quite extensive Inquisition trials and processes aimed at denouncing suspected crypto-jews, often analyzing even ones ancestors. Having one distant grandfather being a New Christian could be enough to disqualify you from many offices or opportunities.

 

To go back to the Orders and their role in this.

First, the fact was that one of the key requirements to enter the order was to already be a nobleman, of pure blood, with not even manual laborers in immediate family history.

But it is also a fact that these requirements were often disregarded for men who distinguished themselves (basically choice of the Crown)

And once one would be "in", they and their offspring would now be considered as "pure", and they did not have to prove their ancestry "purity" any further (in theory). Becoming a member of an order was thus a way to ensure your family safety from prosecution under Inquisition (unless you really anger them, then it would not be enough)

Similar thing could be applied for non nobility. Admission to Order would automatically grant nobility and knighthood to the new member, which when conferred to common men would mean alleviation in status, even if it was to status of only the minorest nobility. From there they would be in a better position then previously and would have access to a whole new social world.

Crown had on many occasions rewarded ordinary men involved in Discoveries in that way, and plenty of distinguished pilots became noblemen and a knights through the Orders. The same often were given to important merchantmen and financiers, especially the ones loaning and investing to Crown ventures.

Even for men already in noble status, admission to Order meant a social status higher then being without one, potentially climbing the social ladder of nobility to a higher point, allowing alliances and marriages with more richer families, sort of codified networking scheme.

 

In the end, membership in the Orders was prestigious and offered many benefits, and applying for it was sort of a normal procedure and expectation of all men working for the Crown once they think they deserve it. Crown supported this and use it to its advantage.

 

Sources

State finance, war and redistribution in Portugal, 1249-1527 by Antonio Maria Braga de Macedo de Castro Henriques

The Military Orders and the Nobility in Portugal, 1500-1800, by Fernanda Olival

Evolution of the Portuguese Order of Santiago, 1492-1600, by Francis A. Dutra

The Social and Economic World of Portugal's Elite Seafarers, 1481-1600, by Francis A. Dutra