Like George says, "If you ain't breakin' nothin', you ain't learnin' nothin"!
I know Peerless made a bit heavier one, cast iron housing. Internals are all the same, however. But I would think the cast iron housing would have a better chance of staying true when heated, as aluminum expands at three times the rate of iron.
However, and to be honest, I have not yet spun my RAGB yet, as I still haven't finished my FX/S build. Therefore I don't know what breaks in these units. The big weakness I see is the miter gears, in that they have a rather limited tooth contact pattern. If you were to find a gearbox that had helical gears which would spread the load across more teeth, I would think you would have a stronger piece. And if that means I would have to cut a hole to let a larger gearbox fit, then so be it.