Sometimes I feel that old :/
Spain has a gold mine so their income is superb. They inherit burgundy, PU Aragon, PU Naples, and have stronger military ideas than France for the first half of the game. They even have a small chance of getting Portugal in a PU which is huge if Portugal makes a bunch of colonial nations. They are poised to dominate colonially. They are a lucky nation until 1700. Now you want to give them an event similar to janissaries or simply add +10% infantry combat ability. I just don't think they need it.
First, Spain's gold income is insignificant; the AI does not know how to prioritize development, and France's development is so superior to Castile's that it doesn't change anything early game.
Secondly, while the Iberian Union is highly likely to happen, AI Castile still often ends up in a war with Aragon, or Aragon ends up in a war with France or someone else that makes them loose Naples as a PU. AI Castile almost never inherits Burgundy - whereas France is guaranteed to get a share, in addition to all the cores it starts out with - which I'm not exactly complaining about. I have only seen the Portuguese vassalization event once, and that was playing as Castile and actively pursuing it. Nevermind all the free cores and claims the Ottomans get.
The idea that their ideas are better than France's early on is a misconception; yes, +15% Land Morale is extremely powerful early game, but it's rarely actually able to be used by AI Castile in a French-Castile war. In the first few decades both are occupied by other issues; France with conquering England and Provence, and Castile with North Africa and Aragon. The difference being that France gets about 100+ development easily into their nation - often free due to cores - which makes them even stronger, while North Africa is more trouble than it's worth and Aragon either ends up in a PU or the amount of development Castile gets is insignificant compared to France's. Secondly, Castile's starting ruler and heir are absolutely atrocious, while France's are significantly better. Between this and the Castilian Civil War disaster Castile is more often than not slammed with, Castile is almost guaranteed to be behind in the tech and idea races by the time they actually come to blows with France. That France unlocks Elan as it's second idea makes it incredibly easy for it to have by the first time they fight, which not only negates but edges out Castile's tradition. Secondly, Discipline is not exactly useful early game, and certainly not as useful as Frances +20% National Manpower tradition which allows them to take full advantage of their developmental superiority. Not to mention France's +1 Diplomatic Reputation, which allows them to form silly alliances at start that their vassals normally would have prevented, which means Castile can easily be dogpiled in both Quality and Quantity too.
If you don't believe me, perhaps we should actually take a look at their NIs:
France
Traditions:
+20% National manpower modifier
+1 Diplomatic reputation
French Language in All courts
+1 Diplomatic relations
Elan!
+20% Morale of armies
Estates General
+10% National tax modifier
Native Trading Principles
−50% Native uprising chance
+50% Native assimilation
Vauban Fortifications
−20% Fort maintenance
The Philosophes
−10% Technology cost
Liberté, Égalité, Fraternité
+2 Tolerance of heretics
+2 Tolerance of heathens
Ambitions:
+5% Discipline
Spain / 
Castile
Traditions:
+15% Morale of armies
+1 Missionary
The Reconquista
+5% Discipline
Spanish Inquisition
+2% Missionary strength
Inter Caetera
Can fabricate claims on any overseas province, provided it is overseas for its owner
+1 Colonists
Devout Catholicism
+2 Yearly Papal influence
Treasure Fleet
+10% Provincial trade power modifier
+15% Global tariffs
A Spanish Armada
+10% National sailors modifier
+10% Heavy ship combat ability
Siglo De Oro
+1 Yearly prestige
Ambitions:
+25 Global settler increase
As you can clearly see, not only does France cancel out Spain in quality in every area, but they
exceed them in quality with Elan and easily surpass them numerically - both militarily and economically - of which is perfectly acceptable. The only thing that Spain does have over France is naval ideas, which are usually worthless when fighting France.
Secondly, you of all people should know that saying that Castile has better quality ideas for the "first half" of the game is untrue; you made a thread a few days ago about how quickly NIs can be filled up, and France usually fills theirs up more quickly the Castile's.
And yes, while Castile is
poised to dominate colonially, they often do not in the AI's hands; Portugal usually beats them to the Caribbean, while France or England usually takes Brazil, both of which are the most useful Colonial regions, and Spain won't colonize there due to ToT. This usually leaves Spain to the less than valuable Mexico region, which until they conquer the Mesos is often worthless (and Portugal usually goes for them as well), and forces them to go into the Great Plains and California. This is, again, in part due to their horrible starting leaders which leave them in the dust compared to their colonizing neighbors. Castile being a lucky nation is irrelevant; so is France.
Now, I can already hear the retort; "in the hands of the player..."
anything can be overpowered or outwit the AI. We do not measure a human against an AI in terms of determining nations capabilities when making balancing decisions, we measure an AI nation against an AI nation. Spain often catches up in most games, but to say the achieve even half the things you say they can, let alone half the stuff they did historically, as an AI is at best a misconception.
Finally, I love the double-standard you have; 'it's perfectly fine for the quality of the Ottoman's elite units to be represented, but not Spain's because I don't think they need it'. The Ottomans get +5% Discipline, +15% Cavalry Combat Ability, +20% Manpower Recovery Speed, and +33% National Forcelimit Modifier in their NIs alone, Devershime throws on +10% National Manpower Modifier and gives an event that provides a free
+50 Army Tradition, Enderun gives them either +2.5% Discipline or +10% Cavalry Combat ability for ten years, Military Reforms give them either +10% Inf Combat, +5% Inf Combat and +10% Galley Combat or +20% Galley Combat for twenty years, the Janissaries give them a whooping 10% manpower recovery speed, +10% infantry combat ability, +5% discipline
indefinitely, and their other NIs and events mean they can easily absorb large tracts of land and make the most out of them economically, and they almost never fall behind technologically. Finally, Islamic Piety almost completely negates Spain's Morale advantage and only makes the Ottoman's superior quantity even worse.
Spain gets squat to represent the quality of its armies outside its NIs - not a single event or decision. +10% Infantry Combat ability will not unbalance the game or make Spain too powerful in comparison to France or the Ottomans.
Edit: And there's no way you read this in the two minutes between me posting it and you downvoting it.
