Nowadays, Silver status can be bought with an AMEX DL CC. $99/year gets you Zone 2 boarding (same) + 1 free checked bag (same). The only thing you're missing is 25% bonus miles (which at 25-50K a year is only 6-12K miles) and upgrades (do you even get upgrades as a silver?).
I find these things would be the same across all the legacies ... credit card holding = most of the lowest tier elite's benefits. Not worth an MR that's more than the price of the credit card.