You gotta remember, first of all, that Cooper from his point of view, been away for several years himself. Even before his team reached the wormhole at the beginning that was already 2 years. I am sorry, maybe you have excellent memories but I struggle remembering SPECIFICS of things that happened even just a week ago, let alone a number of years ago. So, Cooper, who's already emotional and FINALLY seeing things from little Murph's perspective, couldn't possibly remember details of himself. It's almost like Scooge and the ghost of Christmas Past, he witnessing how ignorant he was for abandoning his child like that and was hoping he could change the past.
This was all before him realizing that "THEY" didn't want him to change the past but help form the future. The film already stated that nothing is capable in changing the past,when they happened they happened. But you can already plant seeds to the future. Basically a cause & effect.
As for the brief reunion, I agree it was ineffective on an emotional level, but story-wise it was perfectly fine. You have to understand, as stated in one of her videos to him, she long gotten passed him being away. At her old age though, she believed that one day she will see him again before she died. So, her life was complete when she finally reunited. She was on the her deathbed already and got her own family. Them two are basically strangers and Cooper like an outsider. Also, Cooper didn't want to be on that space station no how, for the same reasons as that he had while on Earth, he's an explorer by nature, that's all he really cared of doing. Being on that station he lacked the sense of purpose. Murphy giving him the okay was ALL he wanted which he NEVER gotten before the last time. So, her okay gave him the incentive to dip out and travel.
As for Anne Hathaway., yea. she'll be an old fossil. If she's still alive. But this was merely an excuse to give Cooper the okay to leave out and explore like he wanted to.
