Hi. I've also been having the exact same problem with my RT-N16.
Funny about the power comment though: The reboots I'm seeing are seemingly random and I've had several other routers blow-up on me in this place. All this had me considering the possibility of bad power -Those wall adapters being so cheap and all…
I initially forgot to mount the usb with noatime, but after doing so it definitely became noticeably more stable.
Now I'm running optware on flash and dansgaurdian/squid for content filtering. Under the heavy load of several wireless clients it still reboots -Mind you my load is a little insane at that point.
I'm going to save the syslogs to see if I can reveal anything else interesting.
I look forward to learning what others are able to come up with regarding spontaneous reboots.