In SaGa Frontier 2, after having bad luck with a few item drops (notably the Granite Staff and Golden Axe, which I ended up hacking in), and having no luck learning Soul Hymn against the Ant Commanders, I decided to continue anyway...
...and I learned Soul Hymn against the Fire Lord in the Old Battlefield on the first try. Now I believe I have every Art except for Thousand Cross, which it a pain to learn and might not be worth it.
As for Soul Hymn, it's a really good spell. It casts Regenerate and boosts Morale on the entire party; in a game where you don't get any multi-target healing spells, this is, needless to say, quite useful. It does mean I have to avoid equipment that protects against sonic, however. (You *can* heal without using a turn by simply using the Recover HP option, but that costs LP, which is not easy to restore, and which you need to conserve during the rather long and difficult final battle.) (Soul Hymn is probably the hardest Art in the game to learn, in any case.)