I doubt "looking" through the iPhoto libarary package can do any harm, so long as you don't delete/add/move files. Just copy the files you need and paste them in another location.
If your really serious about managing thousands of photos efficiently you should move up to Lightroom. iPhoto saves every edit as a separate jpg (or tiff, if you're starting with RAW), which quickly results in a lot of bloat. Lightroom does nondestructive editing, meaning your original remains intact and no duplicates are created. All the eidts are kept in a catalogue file that is less than a tenth the size of an en equivalent iPhoto library containing full size duplicates for each saved edit.
Since I started using Lightroom, I use iPhoto primarily as a Flickr uploader.