Jumping into a thread like this when so much has gone on is difficult. Reading all the prior posts to see what has been suggested and done is difficult and I'm bound to miss something or ask a question that has been asked or suggest something that has been suggested. So bear with me....
You original post seems to indicate that Aperture is constantly generating previews for all the images in your library and that seems to be the direction of the discussion. So my first question have you recently upgraded Aperture and/or the library? Have you recently imported a large number of images into Aperture all in one shot?
Normally when you first install Aperture and do your initial image import or upgrade the library the program will have to go through and generate previews for all the images. On a library of 16000 images this could take a while and was why you were asked in a few places if you had waited for this process to complete.
It is obvious when this initial image generation is done, if you open the library and then the activity window the activity window should be empty. If you open Aperture and the activity window shows activity then there is either a problem or the initial preview generation is not complete.
So if you do this, open the library and the activity window and not touch anything else is there anything in the activity window?
Assuming there is no activity at this point you need to select one image and make some trivial adjustment to it, exposure is fine. As you move the exposure slider the activity window will show a few things but finally it will show that is is generating a preview for this one image. Is that what you see?
The generation of previews is a misunderstood aspect of Aperture. The Share previews with iLife and iWork settings in the preference pane has no effect on the generation of previews only with when outside programs will have access to the updated or newly generated previews from this session of Aperture.
Turning off preview generation is a multi step process and depends on which previews you want to turn off. In the preference pane in the preview tab is a setting New project automatically generate previews this does just what it says if unchecked new projects won't generate previews of images automatically.
However that setting only affects new projects. Current projects will still maintain previews. Aperture gives you the ability to turn off previews in all projects or to have previews in some projects and not in others. And of course this all only applies to the automatic generation of previews. Even if you have previews turned off for new projects and all current projects you could still generate previews for individual images.
The project preview settings are got to by going to the Library tab of the inspector and clicking on the gear in the right hand corner

If you select Projects then you control previews for all projects. If you select a single project you control the previews for it

So where does that leave you. first you need to see if there is anything going on when you open Aperture and do nothing. The you need to see if when you adjust a single image does only the preview for that image get updated.
If either of those are not right there is a problem somewhere. Assuming those go OK then we'll need to try some other troubleshooting steps to try and narrow down the cause.
If when you post back you could keep your answers directed at the questions that would make trying to figure this out somewhat easier, thanks.
Anyway this is a lot for you to digest, hope I haven't muddied the waters even more, good luck.
regards