Password protected servers are a pretty good idea, even if you don't like the idea of allowing such things on the Master Server. Hosting without connecting to the MS is just security by obscurity, and if someone knows your IP Address/domain name, and the port you're hosting on, they could cause trouble. Sure, it's not unmanageable, but the option would be nice.
Also, how about password protected player slots? Rather than password protecting the whole game, you could password protect a few slots. If, for example, you wanted to host a 4 player LAN game, but open it up to the Internet for 8 players total, you could password protect the first three slots, but leave the other four open.