Trading Miles (and likely something else) seems like a lateral move to me. Sure, Mayo's younger and a more polished player, but he has truly had a horrendous year so far and we don't know what we'd be dealing with chemistry-wise. Mayo is 6' 4", not terribly athletic, and to me appears to be a player that has traditionally produced but has no fire. I like him, but at this point, we've been watching Miles ever-so-slightly improve and Mayo seems to be the same player or worse as the end of his 1st and/or beginning of his 2nd year. Mayo doesn't board, and he has always been a poor defender. With no fire and no body, he won't likely improve either of those much.
Miles while older still looks like a work in progress to me that the team is comfortable with. Mayo looks to me like a guy that primarily cares about getting his, and he's not even that good at it. I'm probably selling Mayo a bit short, but my primary sentiments stand.
I don't know about Thabeet. He looks like more like Saer Sene than Manute Bol, and I think Bol was a garbage player anyway.