[quote="Arman"]
The perceived balance issue has less to do with power, and more to do with "time in the game." A fighter and similar classes will always be able to "play" in a battle, since they never run out of their ability - staying alive because they have armor, and hitting people with weapons. Clerics may not hit as hard or as often, but at least they have armor. Priestesses may not have fancy spells, but many of their spells last multiple rounds - a concentration spell that lasts 6 rounds is going to keep a priestess in the battle a lot longer than the 3 rounds a third level mage can handle. With no armor, mages have a hard time staying in a battle and not getting killed.
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All other classes, other than Fighter-types, have periods where they don't get to "play" in battle. It's really only a bit more for Mages than it is for Thieves, in fact. Moreover, Fighters also run out of (or low on) hp, which removes them from front-line combat on a regular basis.
Out of curiosity, which spells do you think allow Priest(esse)s to remain in combat? They have no armor and 1d4 hp, just like Mages, and the only vaguely combat spells they have are Command, Light, Protection from Evil, and Sanctuary. The Command spell lasts a single round, Light can be cast once on a single target to maybe blind them (Saving Throw applies), Sanctuary is for avoiding combat, not participating, and Protection from Evil requires them to remain stationary and concentrate, doesn't affect all opponents, and loses its main benefit (Can't Touch This!) if anyone under its protection attacks. They are far more poorly equipped to deal with combat than a typical Mage.
[quote="Arman"]
Not that I'm complaining about armor, mind you - I just want my players to not get left out of a long battle. I realize cantrips probably aren't the perfect answer; however, I'd like to give mages something to remain useful in a fight after they've used their spells.
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One of the main downsides to a Mage is their inability to hang in combat. It's one of the primary balancing tenets of the class (when balance is viewed holistically, and not just as related to combat). ACKS also has the advantage over newer versions in that battles don't last very long, and take up very little real-world time (at least at low levels where you perceive the problem to be).
Keep in mind as well that Mages have Attack Throws largely the same as other classes at 1st level, with only Proficiencies or Ability bonuses making the difference. They are quite capable of attacking with ranged weapons (and melee; that's just much more dangerous).
[quote="Arman"]
As an added note, however, magic missile and other full-level spells have some huge benefits over 0th level spells - no attack throw, and no saving throw. A spell that does 1d4 damage but can be shrugged off with a saving throw is going to do significantly less damage than an auto-hit spell.
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A lot of these limitations are effectively irrelevant when an ability is at-will. Maybe "irrelevant" is too strong a word, but bear with me. Let's say there's an Attack Throw. That means that for a 1st level Mage somewhere between 1/2 to 1/3 of their attacks will hit. Of course, Magic Missile hits every time without fail, so it is obviously better. The trouble is, with an at-will ability, a Mage is likely going to be able to cast it every round of every combat during a day. The 0th level spell is going to end up inflicting far more damage than the Magic Missile will during a day, it'll just do it over a longer period of time. The Magic Missile will still be objectively better, after a fashion, but only once per day.
Now, let's say you're worried about your 0th level spell still being better than Magic Missile, so you provide the target with a Saving Throw on top of requiring an Attack Throw. The Mage's chances to inflict damage are now better with a dart or dagger; why wouldn't they use those? How "magical" does your Mage seem when they spend their time throwing daggers or darts until they run out, then switch to a 0th level spell?
[quote="Arman"]
Additionally, 0th level spells aren't going to scale, and will be almost useless at higher levels. And, finally, they will do a lot less damage than simply striking out with a staff; the only benefit is that they are safer.
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A staff isn't a ranged weapon. A better comparison is with the aforementioned darts and daggers.
Ultimately, it's your game. I personally think there are issues with 0th level spells generally, and 0th level attack spells more specifically, and since you asked, I'm trying to explain why I feel that way. But, if you find it makes your game more fun you should definitely go for it.