I carry a spare magazine and a BUG every day, and my BUG is a pistol that I can "fight" with that feeds off my primary pistol's magazine. If I think that my day is going to be extra "interesting," I carry a second spare magazine (and a second set of cuffs). This can get to be a bit much for everyday carry, but you do what you gotta do. My "work car" has a set of cuffs and a spare magazine in the door pocket, and another spare magazine in the center console. My "go bag" has multiple spare magazines in it, and my plate carrier has three spare handgun magazines.
I had the pleasure of working with some guys who have "seen the elephant" quite a bit, and not a single one of them considers a "basic load" of ammunition to be adequate... I guess that rubbed off on me.
Back to the original question, though, for a non-sworn LEO concealed carrying citizen, I think the question of a BUG or extra spare(s) is a question of dress, carry mode, and capability. Some attire simply doesn't lend itself terribly well to a "fighting" BUG - and people might be better off with more spares. Ankle carry and pocket carry (probably the most prevalent styles of CCW for a "BUG") have severe limitations on the ease of access to the BUG and the capability of BUG you can carry (especially pocket carry). And, frankly, a lot of folks won't train enough with their BUG to be truly effective with it, especially if that BUG is a lightweight, hard-recoiling "un-fun" firearm to shoot.
Having said all that, all the spare magazines in the world won't do you a kitten's worth of good if your primary pistol kittens the bed in the middle of your gunfight, so there's a lot to be said for the BUG, no matter how limited in capability and shootability it is.
So, my answer to the "BUG or more magazines" question is "yes."
Regards,
Kevin