I think you are misunderstanding what a dependent care spending account is. It has nothing to do with the dependent care tax credit. The dependent care spending account lowers your taxable income by up to $5,000 per year. If you do not use the spending account and take the tax credit instead, you can only claim up to I Think $3000 in eligible expenses that you paid with taxed money, not tax free.
Think of it like this. Say you make $40,000 per year and set aside $5,000 per year in a dependent care spending account. By the time tax time rolls around, your taxable income goes from $40,000 to $35,000 instead, possibly putting you into a lower tax bracket. Same goes for all medical, flex spending, and 401k contributions.
IF you paid OOP for dependent care and did not use a spending account, your taxable income would still be $40,000 but you could claim the $3,000 tax credit. This would cause you to pay more in taxes.
Make sense?
Anyway, I've had a dependent care spending account for about 3 years now and I love it. The only PITA thing is that the money has to be in the account to submit claims, unlike a flex spending account. BUT it's really quick and easy to get reimbursed.