They appear to be something along these lines:
+2 to hit (no idea if this mechanic is functional)
+2 to damage
Base damage is the same as the Halberd (2-16), with the +2 bonus it becomes 4-18
When used, casts one of the ranged weapon spells, then gets used up. One source gives it a range of 40 feet. (I recorded the damage of the breath spells, but not of the ranged weapon spells, as they tend not to be particularly useful unless you have infinite uses of them and are playing The Archer's Tune.)

In any case, it's stronger than a Halberd, but not by much, and isn't useful as a ranged weapon since it hits only one enemy and can only be used once. It's not really that interesting, honestly.

Thanks for the info. Without knowing those details I had come to a similar conclusion that it was not a very useful item, but the name Spell Spear made me think that I might be missing something about it related to spells.