Number of Masters is not a problem with either Aperture or the OS, at least within the range I've looked into. I tested a Library with over 400,000 Masters. Performance was the same as much smaller Libraries, with the obvious exceptions ("Photos" takes longer to load; importing 200,000 files can take several days to process, Faces was close to unusable, etc.).
The problems you are encountering seem most likely to be related to your Drobo (as DiploStrat implies). Borrow a 2 TB FW800 or faster external drive and see if you can move your Library. I can't think of any reason you should encounter any problems. (Fwiw, I've moved 1 TB Libraries regularly, but haven't tried anything larger than that.)
Your "unclear" image looks like corrupted by jpeg-artefacts. Did you export them with a preset "jpeg original size"? Then check the value of the quality slider. Anything less then 10 may cause a dramatic loss in quality.
I'd like to simply store my Master Files offsite as suggested so I exported a test group of about 2000 images and imported them back as referenced files.
To store your master image files offsite do not export them and reimport them, but use the Aperture "File -> relocate master" command. This way no image conversion will take place and the quality of the master image file will stay the same.