My small van has two tire options as tire choices:  170/70 14 or 175/75 14.
1.	I am currently driving on 170/70 14 tires.  If I switch to 175/75
14 what will I feel or notice?  Different steering response? road
holding? braking? speedometer reading?
2.	What is the advantage (if any) for going to a 175/75 size?
3.	Hypothetical: If the pressures are the same for the different sizes
will there be a diffence in size of contact patch?
4.	The car manufacturer list pressures for heavy loads and light loads
(driver and passenger).  By using the lesser pressure I get a more
comfortable ride.  I also noticed that when the pressure is "normal"
(for light loads) that the van's braking distance seems to be
shortened.  I assume that this is due to more tire contact patch
surface on the road because as the pressure increases the tire presses
less on the road and when I?m driving with normal pressure that there
is more rubber on the ground and consequently this adds more friction
for better braking.  Am I correct?

I think your van has two tire options because they are almost the same.

Tire technology is a complex science.First of all your tire sizes. The
first number i.e. 170 is the tire width. The second number 70 is the
aspect ratio i.e. 0.7 of the width. The smaller the number the smaller
the tire wall width. This means lower profile better handling because
of less flex in the wall. But it gives a rougher ride.
Tire pressure does change contact area and hence amount of grip.
However, it also changes flex in the wall, heath build up and hence
wear. A low pressure tire will wear more quickly and can suffer a
dramatic wall blow out because of wall fatigue / splits. Correctly
inflated tires give better braking distance than underinflated tires
because energy is not absorbed by the wall flexing and more goes into
breaking. Your tires are fairly close in size and probably not alot of
differnce. Probably tread pattern will count for more.