A few years ago I was making such a version of the game, when Elric basically womped my idea by planning a similar (and superior) project called the Lion War.
His project, which was moving at blazing speed, forced me to rethink my own. There was a brief notion of my project using his a base.
There were some delays in TLW that fortunately gave me some time to actually reconsider my thoughts on the PSP version of the game. Frankly the war of the Lions script is not as good. It's hokey at times, poorly translated, it's full of major errors. However, it provides an iconic and meaningful experience. An experience that WoTL painfully over embellishes and cannot duplicate.
Furthermore, most of the additional scenes and character content actually take away from the story buy sullying it with additional marketing content that was popular at that time.
The onion Knight is cross promotional marketing for Final Fantasy III DS.
Luso and Balthier are cross-promotional marketing for Final Fantasy Tactics A2 and Final Fantasy XII: Revenant Wings. They really have no place in this story and unlike Cloud, the game doesn't even try to explain why they are there.
The Dark Knight is just overpowered, unbalanced, fanservice. The most significant thing about is how difficult it is to unlock it.
The new Delita scenes are buy large irrelevant. You get to play as his character during some new attitude battles with difficulty levels so low that they undermine it undermines the scenes' inclusion as battles rather than just cutscenes.
Off of the top of my head, the only new content of value is the expanded party roster size and this comes with a distorted and stretched out graphics, intense slowdowns, and terrible sound quality.
Save yourself the trouble walk away.