Anything extra would be nice but battle system changes you mentioned are not improvements, it would just break the gameplay. So no, I would not buy it for that.
The only things XIII-2 improved in the battle system department was leader change/KO, no first paradigm animation and the paradigm tweaks/decks. Other than that it was overall watered down and making paradigms was more restrictive due to monsters.
Throw in a New Game+ that would allow the player to retain all the skills he or she has learned on the crystarium, and that should make the first few chapters when doing a new run much more bearable by opening up the battle system much earlier.
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