You are told "good things may happen" if you expand your castle, but beyond the associated Plaza Tickets, what effect does your castle size have?
StreetPass Mii Plaza – Benefits of Expanding Your Castle in Battle Warriors Way
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Best Answer
There are 20 levels to your castle. The first few unlock abilities/perks. Subsequent castle upgrades update these abilities. The abilities you can unlock & upgrade are:
Unlocks:
Upgrades
Source: GameFAQs