Mutch and Marshall are reasonable examples of players who actually developed here and went on to play at a higher level with other clubs, although it didn't go particularly well for either of them.
Caulker came from the Premier League, only played for City in the Premier League and went to another Premier League club. That could hardly be described as development.
As for Bothroyd, he'd already played for two clubs in the Premier League and in Serie A before he came here.
But hey, if these players fit your agenda, then so be it.