I understand what you are saying about what the man pages say about it being enabled by default, but I'm seeing something different on my end. Before, when using any smbpasswd command I would get errors (as if there was no account). After enabling the accounts, the commands will work and I won't get errors. Also, I couldn't see my linux share from Vista. Now I can see it and it even asks me for a network password. The only change I have made was enabling the accounts. Perhaps the man pages are dated, or I have a different version than you, but I am definitely seeing some results by enabling the account. I still can't connect though, Vista is prompting for the connection ID and password and it won't accept either of the Samba IDs and passwords. I made the Vista a dual boot, so I may boot up in Ubuntu and see if it is (yet another) Vista issue. I used to be pretty good with networking XP clients, but Vista is just horrible!
***update*** I have made a connection to Vista, but that's from the Vista side, I turned on "client folder and print sharing" in Vista and now I can see the Vista share. It kept asking me for my name and password on the mint machine when I would click on the Vista folder. It had three options for remembering the password, one was immediately, the next was until logout, and the last was forever. I must have done it 20 times choosing "logout" and it would just reappear. When I chose "forever" I could then see the folder share. I just wanted to add this in case anyone else was having the same issue. I still can't see mint from Vista though. I've restarted the samba services & rechecked all your instructions on the smb.conf file and can't find anything wrong.
Mint 17.2 with Cinnamon on top of a Dell D620 laptop.