Is Hex worth it at high levels?

[Psyren]

Evil Eye
Prerequisite: must know hex.
When you cast hex, you may choose to have your left eye take on a supernatural appearance denoting its vile power. It may have its sclera turn black or crimson, continually drip tears of blood, glow with power, or any other mark of its supernatural charge. If you do, you may cast it without components (though the eye's transformation makes it obvious you're casting a spell) and as if cast from a spell slot one level higher. As long as your evil eye is showing, you may concentrate on other spells or effects while maintaining concentration on hex. If your concentration is broken, it is broken for all things you are concentrating on at once.



Also added +1 spell slot level, basically allowing somebody investing in an invocation for hex to get 8 hours out of it at level 3. I consider the further upgrade at a higher level to 24 hours to be a much less significant jump, even though it definitely has utility.

Works for me.

I'd argue you don't even need the parenthetical; as long as the eye is obviously weird/supernatural, anyone who can see it has a chance to figure out what it means (likely an Arcana check, or automatic for other Warlocks etc.)

Every spell in the game, no matter how (un)detectable is it supposed to be, has a components that make it perceivable when it is cast, unless you're a sorcerer with Subtle spell metamagic (or get around them in some other way). Because that's how 5e spells work. If a subsequent action granted by the spell is supposed to be detectable, it must be somehow indicated in the spell's description.

There's nothing in Hex's description that placing of the curse is noticeable in any way. Suggestion and Command, in contrast, require you to speak to the target, making them noticeable even if you manage to hide the casting itself.

I know/agree that any spell with components is perceptible, but verbal components are a different level of that. Sage Advice actually covers both examples you just listed:

Is the sentence of suggestion in the suggestion spell the verbal component, or is the verbal component separate?

Verbal components are mystic words, not normal speech. The spell’s suggestion is an intelligible utterance that is separate from the verbal component. The command spell is the simplest example of this principle. The utterance of the verbal component is separate from, and precedes, any verbal utterance that would bring about the spell’s effect.

To a layperson, suddenly spouting "mystic words" mid-conversation is bound to be not just noticeable but suspicious, even if they don't know exactly what you did.