Dying star?

[Ryushikaze]

Rinoa waving her finger at the Star in the beginning and the ending definitely wasn't a coincidence. At the ending, she waves her finger at the star to symbolise the moment they've met from the beginning.

The link there is Rinoa's habit. Not the star. Nor is it a 'symbol', it's a reference.

The moon looks about the same as the one in the present era. Yet, the star looks red. That star being red takes place outside of her castle.

And again, this is absolutely no problem to an 'atmospheric discoloration' explanation.

Visuals are always meaningful if they keep showing up in certain areas of the game, apparently.

This visual does not 'keep showing up' so, by even by that logic, it's meaningless.
Not that your argument is evidence, of course.