These days I visit a handfull of sites a year and get a *lot* more out of it than the days when I tried to fit in twenty stone circles in a day, racing round with my maps.
It's not about quantity, it's about being there and taking time to drink in the whole thing.
The greatest enjoyment I've had has been visiting some of the "difficult" sites on Dartmoor.... mainly White Moor circle and Kiss-in-the-Ring circle. The long walks, spectacular views, and chance to linger make for a real sense of pilgrimage and adventure.
As a photographer, I find that the act of taking pictures actually engages me more with a monument. It makes me look at each stone closely, view them from different angles, and consider how they interact with the landscape around them. Of course, I'm sure there are some "click and run" photographers for whom the act of photography actually diminishes the experience at an ancient site, but I don't fall into that camp. Personally, I love the play of light, and the way stones have unique looks at each time of day and in different weather.
My favourite site for soaking up the ambience is Scorhill. It's easily accessible for a Dartmoor circle, and the location is absolutely perfect. Views to kill for and few visitors. It's a great place to spend an afternoon with a book and a picnic, just relaxing and enjoying the simple pleasure of being there.