Ah, you already had it! Yes, that is what I meant. I never found it because I never venture into the ServerInfo window as I can get all the information from the Servers and Players tabs as well.
Implementing autojoin in the "Server is full"-dialogue makes sense to me though... You can think about it, if it's easy to do and if people'd like it.
Personally I'd remove the ServerInfo window altogether, bind middle-click to Refresh All again, and bring back AutoRefresh Selected Servers. But maybe that's just me.