Doesn't SS as we presently have it do a pretty good job of doing this? It provides a baseline income that allows oldsters to survive. People who haven't earned a lot during their working years don't get a huge SS check, but it's a fairly large percentage of what they brought home while working. People who earned a lot get a SS check that is much smaller than what they brought home when working, but it's still enough to live on, and maybe more than many workers earn. Higher earners subsidize low earners, but everyone gets a check.
If SS is sufficient, why do we hear about all these complaints about the lack of pensions? There is no minimum to SS, and people who work a combination of low wage and fewer years will get little. I recall seeing on SS.GOV site a statement that if the benefit is less than $1, they will not bother to send out a check.
Currently, people with SS benefit less than SSI can go claim the latter, but that is means-tested, and to a very low level (I do not know that off-hand).
If we went to a means-tested system, the government would need to be far more intrusive to determine who has "means," the SS program would lose a lot of public support, and people close to qualifying for the means-tested benefits would have lots of incentive to the spend down their stash (put the whole wad on red or black--it's a win-win!) or otherwise hide it (give it to the kids as a loan--"pay me back with zero interest over the next 10 years").
I agree that it is a big potential for abuse, similar to abuse of SSI right now, or it can get worse because it is easier to claim with the higher asset level as allowed by the Australian system.
If a person wants more than SS will provide, then they will need to save their money. The best way to "unshackle the people who can take care of themselves" is to let them take their d@*n money home and save it/invest it as they see fit...
That's what we do now. And I have no problem with that. I even retired early, as most people here did. But these soft-hearted people keep saying that the dumb people who do not save need to be forced to save. Or perhaps they want the savers to share?
What the Australians did was in effect privatizating their SS system, and unify the IRA, 401k, 403b, FERS, etc... into a national uniform plan. This, I don't think you have a problem with. The sticky problem is how to take care of the people who do not make enough, and to prevent abuse.
By the way, Chile also privatized its SS, something along the same philosophy of the Australian system, but I know even less details of this.