My primary concern with moving a 601kg+ aircraft to RAA is "what happens if CASA decides it's a bad idea and restricts them to 600kg again?"
How hard is it to move a PA28 or C172 back to the VH register when it's been on RA, especially when a thousand other owners are trying to do the same thing simultaneously? If it's been maintained by someone other than a LAME, will CASA insist on a complete strip-down and rebuild by a LAME before it can be VH-registered again? That might sound insane, but I wouldn't rule it out when the goal is "safety at all costs".
I wouldn't move a plane over to RA register unless I already owned the plane but could no longer meet the CASA medical standard. In that case, the risk would be worthwhile. In any other case, I'd stick with sub-600kg for RAA and stick with VH registration for anything else.