Generally, and not only in Hudson, you should install a plugin to a tool you use only if it really brings a feature.

About Green ball plugin, not only, there’s no feature enhancement, but it’s an accessibility regression : color blind person don’t easily differentiate red and green. To have an idea of how blid color persons "see" this two colors, just take a look at this post : Great UI: Clarity and Color on the Presentation Layer, and learn good use of colors for your UIs.

So, just keep Hudson with blue ball and really useful plugins.