It’s good to see a sensible discussion and some interesting questions being asked.
I believe that anybody who takes geocaching seriously should always endeavour to help the cache owners. I now always carry kitchen roll to dry out caches and spare logs to replace those that are beyond signing, because they are too wet. I would never take away a full dry log as the cache owner may want it but will always take away saturated logs as they will be a source of new moisture in the cache. I always log what I have done and ask the CO if they want the log I have removed. So far not one has wanted a saturated log back. If the cache is cracked or of really poor quality then there is little point of adding a new log as that too will become saturated.
As I asked in my original post, what is the difference between a cache and litter? Dartmoor IS different because of the preponderance of cheap plastic boxes (ice-cream containers!) aspiring to be letterboxes, but we know they are not. Surely we need to differentiate our geocaches from this sort of litter and make it clear to the finder that they have actually found a geocache and what it means. I also believe that a properly labelled geocache will better protect travel bugs and geocoins from being stolen if the finder believes that this is a part of a bigger and properly organised activity. Without the label and possible stash card they will have no idea what they have found.