So fury causes "Creatures and people up to level 6 will attack anything nearby for 30 seconds" and Calm causes "Creatures and people up to level 9 won't fight for 30 seconds"

So with these descriptions, does that mean that these two spells are useless after level 6 and level 9 respectively?

Dual casting makes them more powerful as do the perks, and the apprentice/adept/expert spells get more powerful.
I'm level 59 now and my expert level spells still work on everything if you dual-cast them, and they are wide radius aoe.

I understand that, but what I dont understand is why the spell says up to level 6. Does that mean, if I am level 7 and try to use the spell that it wont work? Why does it say level 6 or level 9? It just seems that the spell is kinda useless if its only going to work on creatures up to those certain levels. You are only in those low levels for so long. Why have spells that I am only going to be able to use for a short time.

It means enemies up to that level. Bandits are level 3 IIRC but Bandit Looters etc are a much higher level. There is no ingame way to tell if it works beyond trial and error.

You need the perks that work with the given skill. If you have all the perks and dual cast, your spells will work on almost every enemy in the game even at level 81

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I have a question about this:
If I use frenzy single casted but fully perked, what level of enemies does this work on? In the description it says 28, (or something like that) but what effect does kindred Mage have on this spell?

http://www.uesp.net/wiki/Skyrim_talk:Illusion

Nothing 100% official but a good idea on how the perks work. They seem to increase the level that the spells work on by a fixed amount, some display the effectivenes in the tooltip. Dual-casting doubles it for the most part. For the most part using the higher tiers (apprentice/adept/expert) are the way to go.

HOWEVER master tier versions DO NOT gain the dual-cast bonus, while the expert versions do. To see what I mean, fully perked and dual-casted expert tier spells will work on NPCs like general Tullius and his epic-tier entourage, but the master tier versions wont.

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