If Mycroft had shown interest years ago, during some time perhaps when Greg and his wife were separated, I think Greg might have responded more wholeheartedly and Mycroft could have remained confident in his powers. But the whole secret about Sherlock and John had Greg doubting Mycroft's motivation and holding himself back. The equivocal response had Mycroft doubting himself. Thus was my convoluted thinking at any rate!

Here's an aerial photo of Astove Island: wiki (http://en.wikipedia.org/wiki/Astove_Island).