How to show only Ground Plane in EAGLE
To my knowledge EAGLE displays signals and layers, thus if you click show onto the ground signal, it will also highlight areas with all vias, pads and other tracks (depends on what you mean saying "planes").

One trick comes to mind is to make things you want to see separately in another layer, but I am more than sure then EAGLE will have issues connecting layers reporting unnconnected areas and trying to place vias in unwanted places.

Thus I believe you can highlight specific signal, but can not hide all other signals from the layout unless they are in another layer.