No they are not worthless just less effective at stimulating increased strength and myofibrillar hypertrophy. They are, especially in the higher rep range, effective at stimulating sarcoplasmic hypertrophy along with tendon and muscle repair and recovery depending on how they are used. They can also as you already noted activate muscle hypertrophy through other stressors.
Here I want to ask: Are the "uneffective reps" in A SET REALLY WORTHLESS?
For this reason even during the 5s or higher I would usually include a high rep set of some compound exercise that hits all the muscles used during that workout. Now however with the powerlifting routine I’m doing I usually do theses high rep sets in a separate mini workout to add in recovery. However, for aiding recovery concentric only work, like hill sprints, sled pull/push, rock/medicine ball throwing, are likely better.
Male: 51 years old
Bench Press 240 lbs. @ 178 lbs. (12 July 2012)
Power Squat 390 lbs. @ 180 lbs. (10 November 2012)
Deadlift 390 lbs. @ 180 lbs. (27 November 2012)
Total 1020 lbs. (finally made it 16 July 2012)