Whoops! Somehow missed your reply, Jerrod. Decided I needed to update this thread after doing some testing in the lab.
I was looking for an easy way out since I was trying to test CSR after-hours, remotely, and the main concern has been interference from CCI. Although, I will agree that your test methodology is much more complete and ultimately what I should do.
I did some testing in my home lab and noticed that CSR did not have an immediate effect, just like I noted in my original post. However, if you reboot the AP, CSR seems to take effect. The only confirmation I have of this is by testing the output of 'show ap arm neighbors' before/after adding a CSR value and rebooting the AP. After the reboot, several APs below the adjusted receive sensitivity disappeared.
Also, I noticed any associated clients would start having low levels of packet loss immediately after adding the CSR value, but before rebooting. I would've expected 100% packet loss given a CSR of '55'; obviously extreme, but I was trying to get quick results. If I deauthenticated the client, it was then unable to associate to the AP until I got within range. I was rushing this a bit, so I didn't setup a WLAN capture, but I'm sure I wouldn't have seen probe responses. I will try this again tomorrow.
Doh! Could've used your help with some of the outdoor APs we just implemented.
EDIT
On second thought, in the case of the neighboring APs, perhaps ARM is caching neighbor entries for a period of time so it only appears as though the AP is still able to hear neighbors after entering a CSR value. Rebooting would automatically clear this information.