In complex families i often use some calculated parameters which aren't directly applied to any object in the drawing, but are used by other calculated parameters in order to have lighter formulas: why to show these intermediate (type or instance) parameters in the inserted family? I think that a check box (visible/invisible) would be associated with each parameter, so that you can change its visibility state and simplify the editing of type/instances. Moreover, it would be useful to have another field for each parameter, allowing to insert an extended description of the parameter itself: this extended description would be showed in the bottom of the dialog box of the properties of instances or types of the inserted family. So you should have these field for each parameter:
PARAMETER NAME (string)
->NEW PARAMETER DESCRIPTION (string)
->NEW VISIBILITY STATE (boolean)
PARAMETER VALUE (variant)
PARAMETER FORMULA (...)
PARAMETER GROUP (...)