For a fan of the series it is worth it. I eennoy playing it (again on iOS). The story is interesting and gameplay challenging at times. There is a good chance it will eventually be cheaper if you can wait (probably at least a year). If you do wait consider cheaper iOS jrpgs like Fall of Angels, RPGs by Kemco (often on sale for $0.99), Dragon Fantasy, etc...
You might wish to consider Final Fantasy Dimensions. Somehow 3D and oldskool Final Fantasy looks weird to me.
Everyone values money a little differently. I'm not going to tell you it's "worth it". FF4 is one of the most critically acclaimed in the series though. And in my personal opinion 4, 6, and 7 were the best FF has had to offer to date.
+1. If you are into JRPG's, this is one of the titles you should not miss. And the game does't last for hours... it lasts for several dozen of hours. That's a lot of bang for your bucks. And while you're at it, grab The Dark Gate from Kemco, too. It offers a cool job system paired with other nice game mechanics and an enjoyable story.