well that's the effect but I don't think in my case the steps would be equidistant...and they may not even be the same curve/line...but this is a good trick to keep in mind. Maybe it could come in use. I imagine something along the lines of a gradient paint bucket wich you could use to describe change along a direction....
No, that is currently not possible. You can however always create your own art brush stroke that offers this feature. Still a workaround, but works.
As Mylenium suggest it is a long time feature request to have rogressive blends and other progressive effects.
Actually the blend above might be deceiving because there is not enough contrast in the weight this is what it looks like with a more drastic difference between the thinest and thickest weight
You can then expand and ungroup the blend and use the distribute command on the align panel to make the spaces between the paths equal as you thought the blend above seem to be.
I would think one of these is your solution the distance between the graduate strokes can be change in the blend by moving one of the outer strokes which make the blend such as
You then can do this of course
and the this by replacing the spine not sure why one would do this but you could.
You can make those into art brushes to follow curved paths as Mylenium described.
Are you talking about paths which all reside on the same perspective plane? If so, you can draw the line work in the orthographic flat, group it, and then employ Effect>3D>Rotate (not Revolve) to "project" it onto a perspective plane. You can then put the Group in Isolation Mode and continue to draw into the Group:
3D Effect outlines strokes in order to make them scale. (There should be an option to turn this behavior off when you don't want it, as I often don't.)
One of Illustrator's fundamentally poor interface schemes is the cumbersome way you have to edit objects that have live effects applied. They are "invisible" unless selected, so you have to continually "grope in the dark" for the object you want to edit. That in itself is further exacerbated by Illustrator's hideous "direct selection" scheme.
Workarounds for that are to use the original ortho drawing to define a Symbol, and then apply the 3D Rotate Effect to an instance of the Symbol. Then, you can perform editing on the Symbol itself, and actually see what you are doing. Alternatively, switch to Outline View to edit the ortho. (The problem there is, Group Isolation Mode inexplicably doesn't work in Outline View, so you have to resort to Cut/PasteInFront to get any new objects you add into the right Group.
Using Symbols, you could devise a method for drawings with multiple planes. For example, for three perpendicular planes, you could:
1. Draw a red-stroked square. Use it to Define a Symbol.
2. Duplicate the Symbol twice, color one of the duplicates green, the other blue.
3. Apply the same 3D Rotate perspective to all three Instances, using Off Axis Front orientation.
4. Select the green Instance. Edit its 3D Rotate Appearance, numerically rotating the proxy cube 90 degrees about one axis.
5. Select the blue Instance. Edit its 3D Rotate Appearance, numerically rotating the proxy cube 90 degrees about two axes.
6. Center align the three Instances.
Now, by editing those three Symbols, you can draw paths into the three perpendicular planes.
All this is quite cumbersome and awkward compared to a program that has a proper interface designed specifically for 2D perspective construction (see FreeHand), especially given that Illustrator's 3D Effect does not allow you to position multiple objects at different locations/orientations in the same 3D coordinate system. But the effort does yield the lighter-stroke-weights-in-the-distance you want.