Two part question here:

It seems flying out from either FSD or OMA next Tuesday, the 24th to ATL then flying out of ATL to either or is ridiculously expensive at $758.40 out of OMA and $1200+ out of FSD. Now, should I use use 67,000 miles flying out of OMA while FSD is 124k. I'm Delta only but at what point do you fly a different carrier or use MILES instead of paying cash or do you just say forget Delta and fly a different carrier which is half the cost out of OMA