Question: Are we doing more harm than good, considering how energy/resource intensive the comb drawing process is? To conserve the bees' efforts, can the capped drone comb be uncapped (scraped open?) and placed back in the hive ? Would the bees clean out the cells for subsequent laying of drone eggs by the queen?
Answer: what you are gaining (good mite control without use of a chemical) outweighs harm. Yes it "costs" bees to draw comb so you might have a somewhat lower honey harvest possibility. What is more valuable - less mites (chemically-free controlled) vs a bit more honey? One way to "salvage" the drone cells is to remove the cappings of the drone cells (using a serrated knife) and shake the pupae out of the comb. Sometimes this will mean the entire comb comes out since it might not be anchored well but if the drone pupae comes out with cell more or less intact you have gained. Just removing the cappings with the knife may mean the bees finish the work - however mature female mites in uncapped cells will seek to escape and thus you might slow mite reproduction but not seriously interfere with it - mites that escape (they run out as bees seek to remove the pupa and stay on their new host until they can transfer to another "nurse" bee) will seek another cell to invade and start their reproduction all over vs if you remove the drone capped brood and feed to chickens they are dead. Alternately freeze the drone brood for day or two - this kills the mites inside then open cappings with serrated knife and the bees will clean out the cells. I would feed the chickens as much of the drone brood as possible. Frozen frames with cappings opened when removed from the freezer and then shaken will mean the frozen pupae will fall out - thaw and then give to chickens. Cells ripped or torn will be repaired by the bees (vs having to start all over again - experiment with how much of the capping to remove - even a cell half drawn will save the bees work.
Question: Overall, do drone frames help? What are the best practices for them?
Answer: YES. You save on chemical use in hive You kill reproducing mites when their numbers are expanding in the spring (as you state this only works in the spring when bees "want" to raise drones.). Chemicals like oxalic and Hopguard only kill phoretic mites, Formic acid kills queens or stops queen egg laying and harms brood and Apivar is absorbed into the beeswax. Drone brood removal is a win win win. You are using them as the Best Management Practice.