Reduce the file size of Masters
More than 75% of my photos are not adjusted or starred. Yet I preserve them for reference. They should not take up too much space. Rather 400 kB than 4MB.
After a lot of searching on the web and much discouragement and many misleading tips I found a really good solution for this.
In Aperture:
Step 1: make a smart album which contains all your photos for which you do not need fat masters.
Step 2: select them all and do File->Relocate Masters (and select a new or empty directory to collect the masters in).
Outside Aperture:
Step 3: batch resize the relocated masters. I used ImageMagick (chances are that you have it already on your Mac) (the relevant command is mogrify). This is a command line tool. Alternatively, you could create an Automator workflow that uses built-in Preview functionality to do the resize. Important: the resized master should have the same name as the original!
Inside Aperture:
Step 4: with the photos of step 2 still selected: do File->Consolidate Masters
Finished: now you have slimmed your masters, while all your metadata (including faces and places) are stil in place. One of the misleading tips was: export and re-import your photos. This will mess up your metadata, especially the metadata that is not included in the jpg file itself.
I am aware that this procedure violates a principle: do not touch the masters. For my purposes, masters are not that important. Often I need very severe crops of my photo's (because the targets are very far away), and I am looking for ways to even crop my masters (have not yet found it).
To me it is not important to adjust and tweak the images, but to manage the metadata, because I collect bird sightings with the aim to do datamining on the collection many years later.
Aperture would become much more useful to me, if it offered more (controlled) ways to modify the masters.
MacBook Pro, Mac OS X (10.6.7)