Disagree, I think worst case scenario the car's value will remain unaffected, however you will increase your potential pool of interested buyers - new buyers always (think they) want a manual and rule out auto without knowing how good they are, and assume you can't have fun in an auto. There are more wanted's for manual's than autos execpt those who are on a tighter budget. If you are selling your manual converted auto at the price of an auto imo it'll sell quicker as those on a budget in the market for an auto will see that they're getting the best of both worlds, a manual with an auto pricetag.