I've done that (AirRadar 2 instead of inSSIDer, as I use a Mac, not a windows device).
Mine still drops to nearly-unusuable levels, to the point that we have an old laptop whose entire job is to sit attached to an ethernet port and let us reboot the router.
We have no other networks nearby (even with AirRadar 2 and a packet-sniffer checking), I've hard-set the channel to 6, and the channel width is set to Full (20 Mhz). We're using WPA2-TKIP encryption, although I may be experimenting with TKIP+AES at some point.
I had a Buffalo technical support agent tell me to go to the simple firmware. I can stop these periods where my wireless network drops to nearly nothing (as in average ping, to our provider's homepage through a wireless connection, of 2034 ms) by flashing the firmware. On the simple firmware, it managed to keep things going long enough to get it out of my 'I can return it to the store' period, and now I'm waiting for Buffalo to actually respond to my RMA request (which went to them at 3 AM Monday morning, 5 AM their time, and has not yet received any response at all).
I'm currently on hold about this with Buffalo, at 47 minutes and waiting and no response. The support issues are not particularly reassuring.