I just saw the two different versions too.
Let me say that the 'I love you' makes more sense to me now, but imo it's not my preferred version. Tres you said this was her last opportunity to 'say anything' - in my opinion she says it and then some, only she doesn't use words. (See what I did there? (Although I think someone already pulled that joke in this thread

))
When he starts walking away saying goodbye, she steps out from being 'mission-Yuna', the one who puts the mission first and herself last. She doesn't want to see him go, can't accept he's leaving; she wants him there so desperately she runs towards him to hold him back, but she can't; it's too late. That's her grand move, and imo it's more powerful than three words. (This is coming from someone who found the hand-holding scene more squeeish than the kissing scene.) The scene that comes after is also very metaphoric. She literally has to pick herself up from the ground, and stand up to face whatever comes in her way. But maybe it was easier getting up this time, because she knows Tidus would be there to support her if he could. She is stronger because of him.
Now here's a thing I noticed - they let Tidus have a few sniffles as the green thingys are surrounding him, but in the JP version it is obvious that after Yuna has gotten up, he is crying. It's emotional for him too, it's not just about Yuna being sad. Then, when Yuna says 'thank you' - OMG by the way, the way she says it, so fragile, it's enough to make me cry already - she's thanking him for being the support she needed - yes, for being an Aeon, in a way - but it's also a way of saying she's a better person because of him, he has helped her realized many things over their journey, and his impressions will not be forgotten, she will be the better person for it. The 'runt blitzball player', has achieved greatness in his life. He's made an impact on her life and imo expressing gratitude for someone who has been there for you is bigger then expressing love, when they won't have a chance to be together and love each other. She's also sorta allowing him to go and have peace and be with his father again - 'I'll be fine because of you'.
(AAAAWWWWW)
That last 'hug' is the final goodbye, a goodbye from things that could have been but never will be. (stfu X-2 I'm not counting you)