Heather - have you considered Elements 6? It DOES have a plug-in architecture, works well with Noise Ninja, and adds several other manipulations that Lightroom doesn't do.
You can then specify Elements as your external editor in the Lightroom preferences, flick the pic out to Elements, do the Noise Ninja limbo, then ooze it back to Lightroom.
You can also try some of Elements' other tricks, like Magic Extractor, etc....
Some fun stuff in there to be sure.
Elements isn't expensive, but does a large amount of what Photoshop does plus some extras that Photoshop doesn't do.
Just a thought....