VizPainter is a maxscript tool to help in animating the visibility track for single or several objects.
This one works with a "brush"( a Sphere Dummy ). Animate the Brush accross your scene, select the object you want to make appear the click on Apply To Selection button. When one of the object is in the sphere radius, the visibility animation start. You can adjust start and end visibility value, duration for the transition and add some random value.
> download VizPainter