I'm in the process of converting/building some equipment, and this thread caught my interest. I Googled and found tons of information. From what I read, it seems as though 15 ppb is the recommended maximum lead concentration in drinking water. A *ton* of information points out that almost all faucets in the home are made of brass, as well as numerous fittings in various parts of commercial water systems.
It seems as though we are constantly exposed to it, and your brew water is already "leaded". The concentration of lead is a function of leach time, so I guess that the little brass surface area in the spigot for an hour or two is very negligible in the big picture.
Edit:
Found this comment at
http://www.xb-70.com/beer/3_tier/:
Removing Lead From Brass
A small amount of lead is added to brass to make it easier to machine, and this can be removed from the surface of your fittings by soaking the brass in a 2:1 mixture of white vinegar and hydrogen peroxide. Soak until the brass takes on the appearance of dull gold (5 to 15 minutes). If the solution starts to turn green, replace it. This process is probably not necessary, but it makes me feel better and it makes the brass look really nifty. (Source: John Palmer.)