Are spells mostly a dubious strategy in Quarriors?
The original Quarriors rules do indeed discourage buying anything except creatures. You've put your finger on the problem: the game is too short for spells to be in the same range of usefulness as creatures.

The solution is in an optional rule in the back of the Quarmageddon rulebook: to score glory, you must cull the creature that scored. (If you want to keep the creature, you can opt to not score it.) This has three effects:


The game is slower.
An early lucky buy of a powerful creature no longer nigh-guarantees victory (though it still helps).
Spells are more worthwhile: buying a spell once means you can use it several times, but buying a creature once means you can only score it once.