One of the problems with modeling tubes is obtaining inductance values for the elements. Take for example the grid structure above for a 3-500Z family of tubes. Can you accurately model the inductance of that component. We can measure interelectrode capacitance directly. Transistors are built to very tight tolerances both mechanically and electrically, it is the nature of the modern processes. When transistors are made in this day and age the amount of doping applied (through ion implantation) is knows to a shocking degree of accuracy. While they are mass produced by the billions transistors are a remarkably precisely built product. You cannot say that for hand assembled vacuum tubes. While hand assembled tubes can for practical purposes be consistent in performance and characteristic, they don't exhibit the same consistent performance as we increase frequency that we see in transistors. I have no doubt such an accurate model for the behavior of a 3-500Z could be developed, the problem arises from the usefulness of such a model outside of academic circles. This is a fifty year old tube and it's application has long been set in stone. It's limitations are well documented and their use even in amateur circles is dying.