I recently took a targeted web survey for Southwest. In the process of rating the various decision factors, I realized just how small a factor the frequent flyer program is compared to schedule, price, and on-time performance. The FF program is a tie-breaker and not much more than that. This is why Herb K. resisted starting a FF program for many years, and it's why we may face serious cutbacks in RR. Devaluations per se are impossible with RR, in that credits cannot be banked for use years later.
Well for me RR played a key role in my formula. It was so easy to earn free tickets on WN by flying from BWI to ALB and those other short hops, then use the free ticket to fly from BWI to LAX. Seats were easy to get and I went out of the way to fly on WN. Prior to that, I would go out of the way to fly on DL as I used the freebees for INTL upgrades. After DL destroyed their FF program (along with most of the others) I pretty much flew all my domestic on WN. When WN killed the FF program, I still flew 75% of of my flights with them, but over time I have drifted. I still prefer WN but not sure I will with the new seating system now how I think WN is headed.
The FF program is important to me, but not enough to cause me not to fly WN in general, but it does play into the formula.