I like being able to name things, but I would never rename my main party. The only thing I would regularly do is get rid of the 'XIII' in Red XIII because I don't believe for a second people would say things like "good morning red thirteen". Also I think I named him Nanaki once just to see if there was any different dialogue in Cosmo Canyon (there isn't and it's slightly funny). I've also toyed with the idea of naming Dagger 'Garnet' and thus completely undermine the idea of changing her name for the purpose of a disguise, but I think the joke would wear thin after an hour or so and I'd regret it.

I think X had a good balance of not allowing you to rename main characters but would allow you to rename aeons. Here's a question: do you think that being able to rename Tidus was a hint that he was being summoned by the Fayth, like an aeon?