I don't think one can categorically state that "winglets are for high lift only" and of no or limited value to longer range aircraft. It all depends on the design of the winglet.
Typically the winglet design is optimised for a specific flight condition - if that condition is takeoff then indeed they probably earn their keep best on shorter legs. But if designed for the cruise case, they will be best suited for long range missions.
There definitely are new designs out there, or in the pipeline, which include winglets, some of which have rather long ranges.