I'm not sure that I can help, but what the...
Soon after buying my iBook 6 months ago, I spent
days scanning my old photos into iPhoto 5, naming them, correcting the dates etc.
Since then, I have chosen (for various reasons) to perform a clean install on several occasions - after saving photos etc, of course. Each time, iPhoto has altered the dates of the photos, although retaining all other data.
Digital images from a camera with an incorrect date and time setting gave the same problem.
Attempts to overcome the problem by changing the creation date (using ResEdit) also failed. It seems that iPhoto has a mind of its own when it comes to dates.
As far as your photo library growing, this may be due to photos being edited. iPhoto maintains an original copy after you edit a photo, thus allowing you to revert to the original.
Before adding camera images to a library, I copy them to my HD, name them, make any changes necessary with Photoshop Elements 3 (more versatile and reliable than iPhoto), and them import them to iPhoto. This way, I minimise the library size.
If you observe what happens in the iPhoto library folder when you import images, you will that they are stored according to year/month/day. For some reason, iPhoto likes to create empty folders, eg. a 2006>03>06 folder which contains nothing but an empty "Thumbs" folder. Although only 8KB in size (the minimum), they certainly help to clutter things up!
By the way, you can maintain any number of libraries. Simply hold down the option key whilst clicking the iPhoto icon in the dock - you will be given the option of creating a new library or selecting an existing one.
iBook G4 Mac OS X (10.4.5)