What is the cause of the voltage drop at various spots along the track? Curves, hills ? Are the areas in question easily divided into blocks? Are they consistent?
Do you prefer to sit back and watch them run, or are you a hands-on operator?
If you are running conventional trains, and if you prefer to let them run without your hands on, why not try an old traditional method, which is to feed the main parts of the ROW through one output of multi-output transformer, such as a ZW (or two or more phased single-output ones) and the areas that require more voltage though a separate output, with a slightly higher setting.
This is much cheaper, is easily fine-tuned for different consists at the beginning of an operating session and doesn't require fancy circuitry. Two ZW's will give you 4 big handles if your layout is that big. Add a few Voltmeters and you've got a nice solution.
