I often crew myself, so I know where you are at. Different spinnakers will certainly behave very differently. The F18 spinnakers are evolving into flatter and flatter kites and as they get flatter, they fly much easier and are more sensitive to small adjustments of the sheet (you can capture a big collapse very easily and quickly). So yes, I agree that different spinnakers have larger or smaller sweet spots.

I see your dilemma on the F16, I really feel that if the skipper is looking at the spinnaker, he/she is getting wildly distracted instead of hunting for speed and letting the crew trim the kite. Of course, singlehanded, you have to keep an eye on the spinnaker. I suspect, however, that once you get some more time on the boat, you will develop a feel in the helm that will tell you how the spinnaker is trimmed without ever looking at it.