Agreed - course density is the biggest factor, but it's also a matter of willingness to drive. I just don't like playing the same course 2-3 times in a row. That's why I get out to Stony Creek abiut once a month even though I have several quality courses that are easier for me to get to.
Dweeb Alert: I wish people would stop referring to Crystal City as a cave. Caves are naturally occurring geologic formations and often have features like stalactites, stalagmites, rock formations, are their own ecosystem, and sometimes species found nowhere else in the world.
Crystal City is a former silica mine... completely man made. It's underground and certainly a unique discing experience, but you wont find natural geologic features like stalactites, stalagmites, helictites, etc. Just clarifying a point.