Wise? Or unwise?

I think it's unwise, even though your bank account probably pays more, so you could make money on the spread. It's a hassle, a distraction, and a small but non-zero risk a payment won't go through or something and you'll end up paying fees or having to spend time getting them reversed. The after-tax earnings on the spread would be under $100 if you borrowed $10k on this card. Focus on doing the stuff that allowed you have a paid-off Mercedes and no debt.