A novel can have too many weirds - I read one this summer (The Invisible Library). The problem often stems from trying to shove too many neato ideas into a limited amount of space, I think.
Oh totally. I should have said, "A book shouldn't have too many weirds." They totally can have too many weirds. I think some writers juggle them better than others, like Ian MacDonald. That dude is made out of weirds.