I Do have a few misspelled domains. I never bought them for the purpose of funneling typo traffic but rather as a way to protect my own domains for squatters.

An Idea is to redirect your traffic from the typo domain using a click tracking script rather than redirecting it directly! This would actually help you identify if that domain is of any use to you or not.

10 Typo Domains X $7 X Multiple Years X 0 Traffic = Bad Idea

10 Typo Domains X $7 X Multiple Years X Good Traffic = Excellent Idea