Im inclined to say if this feels like wasted time, it's probably because (as Ben B. mentioned) you don't actually have a strong sales pitch/ offer to get leads away from your competitors. Maybe you could push back and ask for more compelling offer ideas for these hold outs?
I would also argue for (if you don't have them already) agreed upon criteria for these recycled leads. What "no" reasons should be contacted in 6 months, a year, never again etc. if you can get the management team to clearly outline this, maybe it will help you focus more on the right leads to be recycled.