Consider a rejected take off where it is often the case the RTO position of the auto-brakes is so effective that the ground-speed reduces rapidly, so by the time reverse thrust has spooled up to full reverse the aircraft is below 80 knots where reverse is not that effective.
True,reverse is not that effective at low speed as the autobrakes are designed to decelerate the aircraft at the preset value chosen by the pilots.
With the autobrakes,the reverse thrust simply reduces the brakes force to achieve the preset decelration.
HOWEVER,if the pilot elects to disengage the auto brakes,the reverse up to speed 0 is additive to the stopping force using manual braking.
In fact the difference between max rejected take off using RTO and no reverse and RTO with reverse, is only 170 feet on a dry runway if all actions are carried out promptly. Different of course on wet or slippery runway.
Please dont forget your brakes temperature in your equation...
But in terms of good airmanship, it is possible that high reverse thrust in use at speeds approaching taxi ground speed of (say) 20 knots, could be detrimental to the engines.
It could indeed,the Engine Temp will be higher as less air into the compressor,the lower the speed the bigger chance of FOD being sucked in(eventhough runways should be inspected regularly).
The vortex created by thrust on the CFM is reduced with Headwinds,10 kts HW will destroy the vortex up to the usual taxi max N1 of 40 % and 30kts HW will destroy the vortex up to max take off N1.
So good airmanship dictates to follow boeing recommended practices including their fctm on use of reverse thrust which is at 60 kts IAS,reduce the reverse,to be cancelled by taxi speed.
PF should not rely on a call out to start such an action,but by also scanning his instruments just as one would do when the VR call is made.
When braking action is less than good,reverse can and should be used until taxi speed is achieved and or if runway limited until a full stop is achieved.
The ingestion of potential fod is now not the important factor,not being in an overrun is.
The Variable Bleed Valves are designed to reduce the possibility of engine fod damage during reverse ops.