However, buying MC/VC gift cards is usually a bad deal because the fees are more than the miles are worth.

Although there are routes to get miles into Skymiles, you usually get a terrible devaluation doing it. The best I found was the Choice Hotels Visa, which would get you 1 Skymile for $3. You'd be better off with a cashback card. Depending on the spend level, you might want another Skyteam card, like the Continental MC. You could redeem the miles for travel on Delta, but you wouldn't be able to pool the miles with your Skymiles.