Eclipse plugin development is, I believe a very powerful thing. So powerful and so generic, in fact, that it almost resembles a window manager/platform for any type of application you may wish to create. Indeed, I remember seeing when Mr. Gil was conducting some preliminary research on this, that the benefits gained may come short of the effort needed.
Perhaps a simpler tool? Something designed from the ground up, in Java/Swing? Or perhaps .NET? I hear Mono does wonderful things these days!
Edit: Am I really the only one who thinks that sometimes, the effort of creating a small tool that fits some very specific need is less than trying to integrate a new functionality in the existing application?