For anyone over 60 the rates are ridiculous and most of us that old have decided the option is just not viable. In my opinion (and many others) it's better to keep the dosh in an account and crawl back on the plane to home (if possible) and get treated there because, in all honesty I would not let the jokers here touch me if I had anything serious enough to need that kind of coverage and for all other eventualities just pay as you go - it's dirt cheap.
Now if you need it as proof for your retirement kitas I'm told by a friend that with some travel insurance policies and judicial use of photoshop you can get enough coverage to prove to the Immi you are "THE MAN". Use at your own discretion.