Because the Spanish have the ability to earn Home City shipments earlier, their strategies are quite flexible and often a balanced deck can overcome a purist deck. It is not uncommon for a Spanish player to receive 2-3 Discovery Age shipments, and a Colonial Age shipment shortly after aging up depending on the experience earned from Treasure Guardians or the treasures themselves.
The Spanish explorer's special ability to train War Dogs helps explore the territory early in the game and if the explorer is used as a damage sponge the player can collect some pretty heavily guarded treasures.
The Spanish also have many unique home city improvements that help their army and navy, making them dangerous in a large water map such as the Caribbean. The "Galleon" card increases the Galleon's durability and attack by 30%. The "Armada" card increases all warship durability by 25%, making their Galleons far superior to those of other civilizations. The "Caballeros" card increases the unit damage multiplier of the Lancer by 1, making their attacks deal 4x damage against heavy infantry.
Unlike other civilizations, the Spanish are well-balanced; they have a wide variety of units to quickly adapt to changing enemy armies. Spanish units are relatively effective against cavalry. They also possess three Royal Guard units - Tercios (Royal Guard Pikemen), Espadas (Royal Guard Rodelero) and Garrochistas (Royal Guard Lancers); the Spanish are also the only civilization capable of upgrading Pikemen above Veteran status.
Archaic infantry also have the advantage of being trained significantly faster with the Spanish, due to a unique TEAM card. When combined with Standing Army and Fencing School, Pikemen, Rodeleros and Crossbowmen are trained significantly faster (for the latter, they are instantly trained).
With the addition of the unction card for Missionaries in The War Chiefs, the Spanish are a strong contender in Treaty and Deathmatch games. Units under the effect of unction will typically become the hardest hitting units of their type, yet still possess the same hit points making careful management of units a key to success. But the main weakness of this card is that, if all the missionaries are killed, the unit stats go back to normal again and opponents sometimes may target the missionaries to prevent them from giving an attack boost.
Although they're formidable, the Spanish have some weaknesses. They're excellent at rushing but their defense is somewhat weaker if playing on expansion sets, as they can only send one Fort. All other European civilizations can send two Forts from the Home City. The French can even send three Forts, while the Russians can build one more themselves if a card has been sent.
Their infantry and cavalry are relatively weak compared to other civilizations, as their Royal Guard units fare poorly when not fighting against what they are strong against. The low melee damage of an Imperial Tercio and Espada (even a normal Imperial Halberdier does more damage against non-cavalry) means that other units will need to be fielded in to compensate for their weakness. The Lancer is also a double-edged unit; even though it can beat heavy infantry in battle, heavy infantry can also beat them in battle due to their cavalry multipliers.
The Sioux have the Rifle Rider, which can counter heavy infantry and cavalry as well as artillery. Unction also doesn't make unit strong in overall statistics, which means using their counter unit will be just as effective, hit-points wise, as normal. Compared to Royal Guard units, Unction units hit harder, but have fewer hit points.
Spanish church upgrades should be ignored in a deck as they are rather useless in a battle. Although the church card comes with a heavy infantry hitpoints boost, it drops their speed (like the British's Thin Red Line) which can be problematic if the player attacks an opponent far away or needs to retreat. The two infantry upgrades also don't provide much; 18 Guard Halberdiers and 7 Wild Geese (Spanish Hackapells) usually will not last long without proper management.
Like the Russians, the Spanish can only send one Factory per match, hampering economic progress as the player will need to decide which resource will be the most needed for them. Other civilizations can send two factories and can ramp up resource production twice as fast, making them stronger in an end-game situation.