There is no difference between recouping losses on sunk costs and generating revenue. In both cases you are trying to add to your bottom line by utilizing assets you already have in place.
If SSP had that empty space to use right now do I think they'd put in a disc golf course? I think it would be something they would consider. It is a popular multi-generational activity that is cost effective to install and maintain. Claiming that the sport was purer or better back in the day doesn't really change things, neither does trying to explain why they are charging. The person that they want to reach isn't on these forums reading the boards and taking the sport at least somewhat seriously, they are the true rec players who play occasionally, or with more dedicated friends who take them to courses. Most of those players aren't causing problems. The ones who are will not have a problem walking onto kaposia and playing without paying anyways since they are already willing to break the law and vandalize/litter.
South St. Paul wants people to play Kaposia, if they don't then SSP doesn't generate any revenue there, and they want to use the course to generate revenue. To do that at this point you need to offer a superior product as all the other pay 2 play courses in the cities do. Kaposia doesn't at this time, and it is turning people off Kaposia.