@Arcell, you brought up good points. And I agree, I think any changes should be within reason, designed to add diversity but not radically affect or take away from gameplay. If consequential weather effects were present in ARR, I imagine it along the lines of players being presented with moderately altered conditions or caveats, and even reasonable bonuses. I think it would help to add a degree of depth and variety to battle, and in the long run people may be less likely to feel that fighting throughout the game world is uniform and monotonous.

@Kini Since the most significant battles (as well as dungeons) are instanced, I don't think random weather changes would apply to them. It would probably always be a controlled environment. Though, like your earthday-Titan example, the conditions present during a specific game day is another thing entirely... I'm not all too familiar with XI but those points sound really interesting. Were the weather patterns based on the game days? I hadn't even considered how crafting would be affected, lol. And yeah, I agree with what you said, that the important question to ask is if it adds to the overall experience. If the development team had the motivation and resources to design and implement it at the same level of quality they've been performing, I really think it would add a characteristic sense of "FF-ness."