I feel like Buggy would be more active in trying to Ace in your Buggy Parent AU than he was in canon. Do you think that Buggy being in Ace's made he less self-loathing at himself?
Parent Buggy AU:
Buggy, though goofy, is very perceptive. He would have picked up on who Ace was while taking care of him.
I feel like Buggy sees a lot of his younger self in Ace. Having been on Roger's ship, Buggy knows the feeling of inadequacy, having massive expectations placed on him for being related(crew-wise) to Gold D. Roger. He also understands the self-battle Ace has within himself, questioning if he deserves to even be alive or not, and probably knows that Ace feels guilt for the death of his mother.
Buggy would put a lot of effort trying to stop the self-deprecation going on in Ace's head, telling him that every person deserves to be born, regardless of who their parents are. He also reminds Ace that he is his own person, and therefore is perfectly capable of creating his own path and identity. He would encourage Ace to find his own interests and probably drag him into the world of fashion because he did not want him to become a stinky fashionless man like Shanks.
While I don't think it completely erased the self-loathing, I think the knowledge that someone agreeing that he deserves to live helps him, and also in his eyes, made Buggy his first parental figure.