Curb appeal is more than the lawn and fence. In addition to improving the landscaping, look at the physical condition of the property.
If the roof is aging and only has a few years left, you will get a good return on your money by replacing it and trying to sell for a higher amount.
When a buyer is looking at the house, they will also be adding up what needs to be repaired, and coming out of pocket after they buy the house for a new roof will affect the deal.
Knowing that they will need a new roof after they move in, your potential buyer will most likely submit a low-ball offer.