All it had was a musical arrangement/anime cutscenes. That's pretty much it as otherwise it's still the same game. Same goes with Mega Man 8 with the extras.
If only they put more effort (like enhanced graphical changes, re-arranged enough that it runs on the X4 engine, etc), it would've probably been it's own game.
There's a slight difference in that the Saturn Version of Mega Man 8 despite being entirely the same, actually has bonus GAMEPLAY content, in the form of 2 extra bosses. The other actually more superficial extras are the different Tengu Man track, and the art gallery.
as for X3 and PSX X3, While I can agree that the arranged music was not always the best, some of the original tracks were not quite better. SNES Blizzard Buffalo sounds terrible IMO, and it's arrangement sounds MUCH, much better. To be honest, I don't mind the Arranged tracks at all.
To be honest, X3's grunge guitar obsession is it's biggest problem, and the Re Arranged tracks at least try and bring some different instrumentation. The issue with some of THAT, is that sometimes the Arrangement just sounds way too different, or the musical style it chooses just doesnt fit what the original SNES track was trying to evoke.
Many of the tracks CAN work with guitar. Just not like X3 does it.
And just my opinion, but X3's grungy guitar would have sounded MUCH better on the Genesis, which had a penchant for that kind of thing.