I wonder, though, whether the normalization to 200 calories is very enlightening. For instance, 200 calories from a serving of broccoli is something I could imagine, but 200 calories from, say, parsley?

Sure, there are certain spices and ingredients where it won't be so relevant.

But, At the end of the day, most people want to keep their calories to a minimum while maximizing their nutrients.

"Most people" - I wouldn't be so sure about that...

well, perhaps, most people who look up information like this. ;)

Granted, you could is it to maximize protein in take at a given caloric intake