First, you might get more responses to this if you post it under "General Europe" instead of just Spain, since your question isn't really about Spain itself. Second, no one else knows your financial specifics, like how much "a decent amount" is, so you can expect only general ideas, not tailored advice.
It's not "an awful idea," it might work fine as long as your "decent amount" is enough to meet any foreseeable problems, like a medical emergency or missing a flight home and having to buy new tickets. You might look into travel insurance as an alternative "security blanket." I'm sure you know to notify the bank of your plans and find out your daily withdrawal limit (which you might ask them to increase for the trip). It would be safer for each of you to carry a separate card in case one is lost or stolen.
Limiting yourselves to debit cards will keep you from incurring debt beyond the amount in your account(s), consistent with your good goal of being debt-free. You'll lose the convenience of using credit cards for major purchases, like hotel rooms or fancy dinners or big buys, but you may be able to use debit cards for some of these and for others you'll have to use cash, which might help keep you from spending as much as otherwise.
In other words, the pros and cons seem about the same abroad as at home, but consider travel insurance if your bank balance isn't enough to cover contingencies. Hope that helps.