Michael,
Neat Video is doing the same thing for me – it does a re-render every time any change is applied – even the smallest one. This makes the plugin unusable – and I have a MacPro 8CPU machine. Please if you have found a solution for this, post it. I just wrote on Neat Video’s forum, but this seems like a very bad bug and I am very surprised that no other people report it. It starts Re-Rendering in FCPX the moment a change is made, unlike any other filter out there.