HS track schedules are quite brutal and I think you're one of the few coaches to recognize it. I think you are definitely doing the best thing in the interest of the kids. Also, I think holding the reigns a little tighter will mean their performances will be better in the long term.
I can't recall any scientific studies specific to the HS track season about problems associated with frequent competitive situations without adequate rest. There is however quite a bit of research on overtraining (which this essentially is), the effects of frequent high stress level training, repetitive trauma injuries associated with inadequate rest and recovery; and also studies finding that kids who are not fully developed but exposed to very high training loads may have permanent structural or hormonal changes. There is also tons of anecdotal evidence from experienced HS and college coaches who have found out that most kids cannot handle this kind of a week and still do well either from a performance or injury standpoint. Also, due to the way HS sports are set up in the U.S., most kids (unless they are 1-sport people) typically do not have adequate prep time to really get ready for their sport which means the 3x / week meet schedule is just asking for injury.
Overall, I think if you look at the meet days as really hard practice days and then try to give adequate rest on the non-meet days the HS season can be negotiated reasonably. It's when coaches train hard on the non-meet days where there would be major problems.
Here's a great case-in-point: at LSU, we rarely if ever let kids do 3 events in a meet (other than at really big invites or nationals); and it would be far more likely that we wouldn't even let them do two. We also frequently hold our big guns out of lesser meets altogether because of the reasons listed above.
