@ppoirier - I thought about your answer a bit more. Sorry, if I misunderstood and that what you were driving at was that I can’t really hope to achieve good control, irrespective of the user interface involved (sticks on a TX or UI elements on a smartphone touchscreen), unless I first introduce closed loop motor control? I’m new to this area and just getting to grips with everything that’s involved.
This recent ArduRover related blog entry looks like it might be a great starting point for investigating more sophisticated control (although the described setup, while using ArduRover, does not use encoders).