Many previous studies have been criticised as flawed because many older, established suburbs are walkable (especially if built before broad car ownership) and more affluent anyway. However this study controls for other elements in house values to isolate the impact of walkability on house prices.
Tellingly, it is not a linear relationship: the extra point in WalkScore from 79 to 80 is worth far more than the extra point from 19 to 20 (almost forty times as much!), so if developing or investing in infrastructure and improvement in an already walkable neighbourhood, there is a strong financial incentive to further increase the appeal of walking.
The message from the research is clear: investing in walkability pays dividends.
You can find a summary of the research here.