Good point, even knowing the password for the advanced interface what is the worst that you could do to it? It doesn't let you access any network data or personal details. So you could probably get an idea of how much data I use and a few technical details on the quality of my connection and maybe be able to access my IP address ( which you already have if your seeing the interface). I suppose if you were really nefarious you could probably cause my device to reboot a few times if you wanted to be persistent about it.
It's been a number of years since I've gone into it myself so today I tried to get into the advanced settings again and apparently my connection is being refused I can only see the basic page so I'm assuming I've gotten a firmware update blocking access at some point.