Well, according to my dictionary, its not a mispell, but a variant of the spelling Inquiry. When you do a search for Inquiry vs Enquiry, there is no question that Inquiry is the more used spelling. Although not a mispell, When considering its the alternative spelling and potential market uses, Im going to give it a a $10-20 appraisal. Right now its limited, it could be developed, Im just not sure into what.
Good luck!