Short Answer: Yes, magic is certainly worth it.
Remember that magic is about more than simply tossing battlefield nukes. As others have written, Astral magic is really more for support than for blasting.
Here are several non-battlefield uses of Astral magic:
- quick transportation -> Teleport, Gateway, Astral Travel
- reconnaissance -> Astral Window, Eyes of God
- site-searching -> Acashic Record
- commander-killing -> Mind Hunt
- defense -> Dispel, Dome of Arcane Warding
- dominion-pushing -> Telestic Animates, Juggernauts
- WISH ('nuff said)
Astral magic also offers some nice Construction possibilities: Pendants of Luck, Amulets of Antimagic, Rings of Sorcery and Wizardry (to boost other paths), Spell Foci, Robes of Shadows, and that Shroud thingy to bless your non-sacred commanders.
However, Astral magic can also be handy on the battlefield. Besides the tactics that have already been mentioned, here are a few more:
- Stellar Cascades -> No, it's not as impressive as the Abysian BBQ, but it can be just as effective. Dish out massive AP stun damage to large numbers of badguys. Then your troops can kill them easier....
- Star Fires -> Cheap, simple ... armor-negating damage. Great for opponents with a lot of protection and not many HP.
- Solar Rays -> Reasonably effective anti-undead spell. Kill hordes of zombies.
I can also attest to the effectiveness of the previously-mentioned Mind Burn and/or Soul Slay. Sure, each spell only kills one unit, but that's great against an opponent with expensive, hard-to-kill units. Set up a row of Mystics with Spell Foci (to increase magical penetration) and start zapping.