It has been only somewhat recently that Block-Changer chisels were changed to only actively swing only under the condition that they could actually change their target block.
I was repairing my coils now and realising that I miss some hits from time to time, wasting some energy.
Only being able to use spanners on valid targets would mean no wasted swings from missing a coil/machine (since that wouldn’t happen anymore in principle), and could potentially be extended to only consider as valid targets machines or coils that have at least 1 unit of wear damage, thus preventing needless repair hits on fully repaired blocks.
I don’t think it’d matter, since spanners don’t actually lose durability if there’s no valid target getting hit. I checked that just yesterday on a stone spanner.