Maybe I'm not understanding this question correctly. I see feedback from other agents here suggesting it is MORE of a fire hazard NOT to have the door than it would be if there was a door. From what I've heard in inspections the less the barrier between the house and garage is compromised, the better it is from a fire safety standpoint and the thought about the fumes and CO from the lawn mower and such. If you create an opening between the house and garage, in my mind, would allow more opportunity for a fire or fumes to encroach in to the home. If, for no other reason, than you'd be opening the door and allowing exchange of air between the house and the garage. Please tell me what I'm missing here, agents.
From a market standpoint, it is always better in MN to be able to go from the garage to the house and vice versa in the winter. But, I wouldn't say it's a huge deterrent for resale. It would be more of a minor thing than a major thing. If you want to create a door, do as one of my colleagues suggests here and have a bid done on the door during your inspection period.