Good point! I agree that for some studies the genetic variation is valuable in itself.
Although, when you are doing these studies, is the genetic variation the variable parameter or is dose as well? For example, in a pharmacology study with 100 monkeys, do you use the same dose to test the average effect of the drug on a large variety of genetic makeup? I would argue that testing dose-response testing would benefit from cloned subjects.
Additionally, I predict it would be possible to prescreen the DNA-to-clone for a gene that can cause substantially different reactions. Although, this is purely hypothetical.
Great input @sco!
when you vary the dose, you take groups of animals that receive the same dose. You're right, with clones you would probably need much less animals here. But even so, you would have to test at least one concentration with different animals in addition to that, lest you risk the effect described above again.
But this could - in the end - result in less used animals, depending on the design of the study. Great thought!