One doesn't doubt that winglets pay for themselves over time. But not so much that one would schedule early maintenance to repair them! Their saving is very small- I very much doubt they pay for themselves over a period of a year or two, but over the lifetime of the aeroplane, yes most certainly they do provide a return in fuel saving.
The whole point of this thread is:
They are not aerodynamically important or essential
Their saving is small
It is not worth downtime to repair them