about the only thing you can use 20K for is a one-way upgrade, and even then I think you might need to either have status, or be flying on a business class fare. Still possibly worthwhile for a splurge.
With 49K, you could try buying your next several internet purchases through the NW WorldPerks mall (you can find it via nwa.com). Once you hit 50K, you've got two domestic tickets. Despite NWs historically poor record at award capacity, I managed to snag 2 standard award tix for a long weekend in September DTW/MCO, and I booked the flights only a little over a week ago.
NW's loads have been high, and they've been leading the legacies in RPMs (revenue-passenger-miles---in other words, NW has been flying planes with more people paying higher prices), so they are probably not the next to fall, but they have been losing money.
