Q: What effects do cleverness have upon your reader, when your reader reads the things you wrote?
A: Ask someone more studied than I.
Here, however, are my thoughts.
The story is: rundown carnival. Chain saw weilding demonic clown wants to kill everything.
Cleverness is personable. If your characters, your narrative, is clever, funny, flippant, quippant, and all around hee-hee to read, your audience has something human with which to associate. Make them feel that what they are reading is about and by real people, who like to laugh, and they have an immediate excuse for why the scary things are not real. If they see that, at the drop of a banana skin, everyone--bad guy, good guy, narrator and all--will dissolve into chuckles, which the reader is sharing in, then your reader is able to step back and say, "Hey, this isn't real. The demonic clown with the chain saw is fake, and will not come and get me, because he is, in fact, a good natured comedian, just play-acting at being loony scary. Tra-la-la."
Remove cleverness: Reader becomes afraid of the dark. Without occassional laughs, for no reason but a turn a phrase, without that personable quality, there is no escape. There is less humanity, and the reader sits when the tale is done, and they know that clown is just waiting inside Santa Claus, or their Dad, or in their closet.
The narrative voice knows everything. Cleverness is a sign that the narrative voice knows everything is going to turn out alright in the end, that the story is about the ride and the reader can relax because it has a happy ending. Without cleverness, with a narrator who is frightened, who cannot be clever because he knows the end is messy, your reader doesn't know what will happen, but knows to be afraid.
Yep. Cleverness and fright.