It is a valid concern. I think it is a beneficial feature as long as not overused, therefore I wouldn’t make a big announcement out of this to have all users revisit their old threads to select solutions. Best is to observe how it affects the threads in #help category.
A big plus in Discourse is that we don’t have a score that is always next to the user name. The number of accepted solutions will appear on each user profile page, however it doesn’t grant anything, since the user trust levels (Discourse’s reputation system) are mainly based on read time.