It really depends on the construction of the guitar - when the top bellies, it can lead to loose braces, a popped bridge (had that one happen), etc. On the other hand, I kinda like a bit of belly on an older guitar - I wish I could say it definitively adds to the vintage tone, but sometimes it feels like it does
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I typically have my guitars checked out once over 1 - 2 years - a key checkpoint is the health of the internal structure, given any bellying going on. So - I don't think there is a "correct" answer as much as the fact that bellying has its pros and cons and if you like the guitar, just make sure you get it checked out periodically to ensure that the bellying isn't translating to a big structural issue any time soon...