Is there reason to believe that data, available or possible, from eye tracking is far greater than what is utilized? YES ! :
Computer scientists tell us that ANY similar or exact patterning of visual perception or attention, with _ANY_ overt manifestations, can be captured. Unquestionably much develops from input through the eyes (the MAJOR example: ontogeny); plus, behavior IS PATTERNED (as would be true for any significant biologically-based functioning (and ALL behavior is)). AND, ALL such could/can be found/identified using eye tracking and computer assisted analysis. ANY/ALL. Thus, it would be useful for psychology to capture any/all such. (It would be more constructive to start with analysis including most-all subtle behavior patterns; that avoids at least most unfounded a priori assumptions (actually: presumptions).)
Unlike modern assumptions, little is likely just random; and YET ALSO, for-sure, little is just statistical. (Nature doesn't play dice.)
True, this is self-serving (for me, for my definitely empirical theory) BUT IT IS ALSO TRUE.