Allow varying of parameters other than frequency
Allow the user to set a particular frequency and then vary e.g. resistor values and plot the results, instead of always having to vary frequency.
Could take this a step further and allow multiple parameters to be varied at once.
Could also allow the user to specify a generator for the x-axis, to allow for adaptive simulations, i.e. ones where the next frequency is calculated based on the gradient between the last two, to allow more points to be simulated near where interesting features occur. Could maybe provide such adaptive generators in the toolbox.