If my spouse and I own everything jointly, might a durable power of attorney still be useful?
Absolutely, a spouse does not have the implied authority to act on your behalf as to your important legal rights and property interest. Some financial institutions will allow one spouse to direct a joint account without the jointer of the other spouse. For things, such as real estate, lawsuits, and other important rights; typical you individually will have to represented. The Durable Power of Attorney would authorize you spouse to act in that capacity.