Agreed. I am an appraiser of over 10 years experience. I wouldn't give you much of anything for it, $1,000 maybe $2,000. There's simply no appeal as it's nothing more than a glorified patio with seasonal use. Honestly, the playground sounds as if it would contribute more than the basketball court. More buyers have children than NBA fantasies.
If you plan to keep the home, go for it, if it makes you happy. If you plan to sell within the next few years I'd reccommend against it.