That's interesting, DT reviewers usually listen so I think it does not hurt to send them an occasional polite email when the photos are rejected.
Each photo should be taken case by case, if a photo has some issues that an be fixed then it can be worth resubmitting it although sometimes it's a lost case and that's fair enough. In some cases where I disagreed for the reasons stated for the rejection my photo got approved after I sent an email and stated my case (few cases but still worth trying occasionally).
Sometimes it's better not to argue and simply resubmit it again at a later stage if you think it has potential and is rejected for lack thereof - going through a different reviewer might give a different result.
Finally for non exclusive contributors it's probably better to submit variations to other sites that have a different policy on similar images, in order not to damage the approval ratio at DT - as I think the approval ration influences the image placement in the search engine.
I had the same issues with my collection of "Coat of arms"
I tried to submit them one by one but more of the time they are rejected for the "too many..." Then when I compared my collection with other "flags" contributor, I found one who used the computer generated flag with only the texture of the flag changed (more that hundred...) I was a little bit disappointed at that time.
It seems that the trend/advises from editor is going to a sort of "collage" picture of the same topic. I tried it and it seems to sell well as well.