You do realize the only thing a Genie mini can do that a HR24 cannot is schedule a recording on the Genie? All devices - Genie, mini, and HR24 will be able to see all recordings recorded on either the Genie or the HR24 and there is no difference in monthly cost.
Aha! I did not know that the HR24 could utilize the Genie HD content. Not being able to schedule a recording on the Genie, but still being able to record on the HR24 and watch anything recorded on the Genie would be great for my wife. So, my new summary is:
Genie in the FR to replace the HR21.
Wired mini in the kitchen to replace the HR24.
HR24 to the BR to replace the HR21.
Wireless mini in the den where I presently have no wiring.
My cost should theoretically go up by $9, though that and the fees for the new equipment/installation will depend on what happens when I call Directv. I have seen from reading other threads that this varies considerably.