I absolutely agree, when something physical means this much, it can be a definite sexual turn-on, just looking or thinking about it. And I do believe that those experiencing boobie greed feel that when looking at themselves, maybe imaging their boobs even bigger, and thinking how that would increase their enormous boobie adventures; Beshine has actually come right out and said essentially that.
I have to believe that a girl doesn't know that she has boobie greed until she experiences the ability to expand her boobs. This certainly seems to be the case with both Beshine and Foxy; both had initial goals of 2-3k before feeling the overwhelming urge to keep expanding.
This follows the same path as girls that intentionally gain weight to become enormously fat. I have read accounts and psychological studies that they often don't feel the urge until or unless they gain some weight, then it becomes an overwhelming passion to become extremely fat, usually leading to so fat that they become housebound and need someone to take care of them. And the studies say that their libido often dramatically increases as they are increasingly turned on by their own fat. The last thing they want is to lose weight, because despite the hardships, being excessively fat means so much to them; it is a constant source of happiness because their struggles are a constant affirmation of how fat they are.
I'm certain that both Beshine and Foxy feel the same way about their boobs and that, given the ability, they would keep making them bigger, viewing the increasing hardships of enormous boobie adventures with positive affirmation. We see that with Beshine who admits that there are many things she can no longer do and everything she can do requires altering for the size and weight of her boobs. And yet, she continues to gradually make her boobs bigger, willing to sacrifice more physical movements to have even bigger boobs. She talks about the weight a lot and how it affects her movement and how the movement of her boobs stresses her clothing, but make no mistake, she loves it and wants to experience even more.