there are many Export[] types

you might try exporting the data as 3D data - which will give you columns of values. then maybe use awk(1) or printf(1) after to clean it up. the graphic data may be stored. say x is a graphic, then x[[1]] has a structure (see the Structure of Graphics in the Mathematica book). with that you could generate an array and write it to disk the usual way >>

probably you want to use Export (type lines or something) on the Graphics[] data portion of x will work

You may need to apply Normal[x] first (for some Mathematica plots there is no graphics data unless requested), and in some cases even Normal will not yield a result: in which case your left to DiY.