Question: Different size points for pointplot and transforming to 3d with 2d symbols

I have a set of points and 2 questions

Each point has different values associated with them.  I want each value of the points to be displayed as a specific symbolsize.  The only way I could figure out how to do that was to create a list of the points of one value and set it at a specific size, for example like this.

Suppose pointset a has value 1
a:=[[1,2],[3,4],[5,6],[4,4]]

and suppose pointset b has value 2
b:=[[2,2],[3,3],[4,4],[2,3]]

I think the only way to do what I want is this

with(plots):
a:=pointplot(a,symbol=circle,symbolsize=10,color=red)   # 10 is the default anyway, this is just to explicitly try to show what I'm trying to do
b:=pointplot(b,symbol=cirlce,symbolsize=30,color=green) 
display(a,b);

So for each set of points with a specific value do I need to create a variable to contain those specific points at specific symbolsizes?  or if a 3rd value is in the points is there somehow I could use that in the symbolsize to set the size of the point?

My other question involves transforming the plot to 3d.  When I transform the symbol=cirlce to 3d it becomes a sphere, how do I keep it as a circle?  I'll use the example I have already given to show the points become spheres. 

with(plottools):
3d0:=transform((x,y)->[x,y,0]):
3d1:=transform((x,y)->[x,y,1]):

display(3d0(a),3d1(b));

Better yet, is there a symbol option in pointplot3d that allows symbol=cirlce on the xy plane?  That would actually be better.  Or do I need to create object circles and transform them.  It would be much easier with the symbol option. 

This is probably a bit confusing, I can try to elaborate if it is.