I did the same thing you are doing for a number of years, but somewhere along the way I picked up a meter to use. I found it to be quicker and easier to get the channels adjusted evenly using the meter, and the system sounded more cohesive and uniform afterward. Individual speakers blended in with the rest of the speakers better, and pans seemed a bit more fluid.

There was once a very lengthy, energetic debate here about the benefits of an SPL meter for calibration. A substantial majority of the debate's participants reported finding it to be beneficial. Some people went back and made subtle adjustments after using the meter, of course, but they still found the meter helpful in giving them a relatively even starting point.