I thought the tax thresholds applied to de facto spouses as well - so if you have been living together prior to marraige, whether your name is on one card or not, the actual marraige wouldn't make any difference....? Even if you are a de facto couple, (as opposed to married) you should be declaring your spouse's income, etc at tax time.
Good to know it is easy enough to change your name with Medicare though.
I'm not money minded at all, but yes, you are right, DH and I always declared each other's incomes before we were married, I just know that the medicare lady said it would mean that we'd 'get more money back' somehow
But I am definately not the right person to ask on how it works or what the actual benefit is!