as two points of reference.....

i remember being in Bartons shop many years ago(late-80's) when he was still up in the Montreal area, and saw some SS/AA heads he was working on there.
the intake valve seats were just a very, very thin pencil line.....probably around .015" wide at most, right on the very edge of the valve.

on the other end of the spectrum, that old SBC Pro Stock engine book by Grumpy Jenkins specified the intake seat width to be .100" wide......and that was for a true max effort application.

so whats the right width seat???
its just another example of the many, many things that are engine related that fall into the "it depends" catagory.