The fiber-weave effect depends on multiple factors, and it is a statistical issue. Therefore, I think it unwise to make a categorical statement about a modeling methodology or frequency or routing method related to fiber weave. There is a lot of good information published to describe the problem, how to simulate it (usually the worst case), and how to route traces to mitigate the problem. In just a quick search I found this paper from DesignCon last year.
The abstract states that the problem can be (worst case) as much as 7ps/in, but with some good choice of dielectric material, and some typical manufacturing variation, the skew is less than 1ps/in.
Now the question is about the significance of 1ps/inch in your particular design. You can easily add a few picoseconds worth of T-line in a LineSim schematic to observe the impact of the skew on your circuit. Then you can decide if it is important to model the fiber weave in any particular design.
Another question is, what post-layout simulation tool _can_ simulate the fiber weave geometry? If you have to extract the model of a differential pair to another tool for fiber-weave modeling, why not do it in an easy-to-use tool, LineSim?