I can't speak about the profitability of owning a skate shop and or a skate park but I will say that it's as popular as ever. My home town in south Florida built a city owned and run skate park with a shop. It gets super crowded when it's not too hot out and it's a great place for the kids to hang out. There's also many skaters in there 30s and 40s.
There are several skate parks scattered around Florida and they are all thriving. Like you said, if you find a location where a skate park is needed the locals will support it and if it's good many will travel to skate it. If you build it they will come.
Here's a video I made of my friends at the city owned skate park
http://www.thewoop.com/public_html/s..._Skatepark.mov