There are lots of thoughts and opinions on this issue so I'll just let you know what I do. When I find old equipment, I make sure that the boxes are standard size. I've seen home made boxes that "almost" sit perfect on top of my store bought boxes..but not quite. I also make sure the boxes are OK to use.....no un-repairable splits, no pieces missing on the bottom where they would leave a gap when they sit on top of another box...stuff like that. I don't re-use frames. They go into the fireplace as kindling. I don't re-use comb. That goes into the wax melter. Boxes that are salvageable get re-conditioned. If the frame rests are metal, I pull them off. Both inside and outside gets rough scraped to remove the loose junk like wax moth cocoons, etc. Then, I torch the inside until all the exposed wood has been blackened. I pay particular attention to the corners and the edges. Once they are cool, I sand the outside. Then, they get washed with a mixture of TSP, bleach and a mild soap. Once dry, they get another quick sanding and then primer and paint. It's a lot of work but sometimes, it's worth it compared to buying, shipping, building and finishing. I just finished 11 old boxes like that which will help with my expansion plans for next year.
I replace the metal frame rests if the original would is questionable (rounded or gouged). I also glue / nail any loose corners. Vents that were drilled into the bodies can easily be repaired with a cut dowel.
Obviously, I put new frames and foundation in after all is done. Excluders get torched to remove wax and then washed and edge painted like the boxes. Inner covers get torched and washed. Outer covers and bottom boards get similar treatment.
Hope this helps. Others will have different opinions.
"My wife always wanted girls. Just not thousands and thousands of them......"