On any apt-get or Software-Repository start I always have to enter the PW, however I have it set to remember the PW for the duration of my session that way I only have to enter it once. Maybe you have this set too?
I do have to type the admin pw every time I use the terminal though. So I'd say it's secure enough.
But if you're wanted "stability" like you said, you should go with Mint 13 Maya bc it's based off Ubuntu 12.04 LTS (Long-Term Support), whereas 14 Nadia is 12.10 . Gives you the newer
features but loses some of it's stability *in theory lol*