My experience (maybe a rule of thumb?) is that business class on Delta1 values a skymile at around $0.01 to $0.013. That is not to say there aren't deals but depending on your departure airport and all the other requirements mentioned above. The round trip, advance purchase, Saturday night stay rules are the same as cash tickets and Delta is trying to push Skymiles as currency.

So yeah, if you want to stay with Delta, going for a 1.5% or better cash back credit card and buying your D1 fares might be easier. Plus you earn medallion status and points on those cash fares. With flexibility though comes options like awards via other airlines and Amex or Chase reward points.