A discussion has started up in my group about how you actually use enchantment spells on people without them noticing. A good example is as follows:
Charm Person, one of the good lower level spells for Enchantment has the following:
Components V, S
This means that you need to make clear hand motions and intone clear words. As far as I can tell, you cast this spell and then the first question they would ask is "What did you just do?". It gets even worse when you consider Sow Thoughts. The target at that point has probably just become less friendly to you.
Is it a case that these kind of spells are supposed to be cast from a hidden location or with silent and still and such? Or should they be fine to cast in conversation?
If the solution is that "you need X feat" or such, then why is there a feat tax being applies to an entire, arguably already restrictive, school of magic.
Best Answer
If a creature doesn't want to be noticed casting spells then, yes, the creature must devote resources to doing exactly that, and that includes Enchantment spells. By eliminating the inexpensive material components with the feat Eschew Materials, somatic components with the feat Silent Spell, and verbal components with the feat Still Spell one can cast a spell nearly undetectably--from onlookers1 (an affected creatures still gets that tingling feeling when it succeeds on a saving throw versus a hostile spell and still has a chance to identify the spell cast on it via a Spellcraft skill check). But, yeah, it's difficult to make casting happen stealthily. And it should be.
Your question focuses on the lack of utility of Enchantment spells when the target knows such a spell's been used on it. I'd be more concerned about the increased utility of Evocation spells were they employed in this nearly-impossible-to-determine-the-source fashion.
The Spell Charm Person
The expectation is that spells charm person et al. actually are cast right out in the open--at an approaching potential enemy. And, if the enemy fails the saving throw he very well might ask, "What did you do?" if the creature is unable to identify the spell as it was cast (and most creatures can't). That's when the caster says, "Just a detect spell; don't worry about it," and, as the enemy is now you're friend, he doesn't.
However, I get the sense that your group might want to use the spell charm person against shopkeepers, city guards, buxom barmaids, and other folks in the middle of town in an effort to get free goods, to encourage a slap on the wrist instead of the gallows, to make them pay more attention to you than the muscleheaded barbarians, or whatever. In those cases, casting a spell can be problematic.
I'd urge casters to role-play these events, using minor magics like the spell prestidigitation to instantly clean the shopkeeper's store, shine the guards' shoes, or conjure a gift for the lady instead of whipping out the charm spells. Harnessing the power of the universe to get a 10% discount on swords, to avoid paying a parking ticket, or to get a lady to pay attention to you2 is... excessive.
Casting in the Campaign
I can't know the kind of campaign you're running, but in my campaigns folks are familiar with magic even though most lack ranks in the skills Spellcraft and Knowledge (arcana). Intelligent creatures in civilized areas view spellcasting the same way many contemporary societies view taking out a pistol and waving it around. You want to clear the bar? Start casting a spell. You want folks to run for cover? Start casting a spell. Spells are worse than firearms--nigh undetectable until used and can level cities.
Polite casters in my campaigns quickly learn to warn onlookers that they're casting a spell, explain what the spell is (making Bluff skill checks if necessary), and provide those who want to the opportunity to leave. Impolite casters get grappled or stabbed by folks claiming self-defense.
The campaign needs to establish guidelines for casting spells in populated areas because, yeah, spells are awesome... if you're the caster. Spells are death via a handful of bat guano, throwing horns, and yelling fireball! to everyone else.