Léonie has provided an excellent answer to your question -- I would like to propose a different solution to your problem.
First, though, we should confirm what your problem is. From your post, it seems that your Aperture _organization_ is a mess, and you want to clean it up. Your proposed solution is to start with a new Aperture Library, and populate it with the Images (including adjustments) that are in your current Library.
An important thing to take from this is that Aperture is _working well_, just, from a human perspective, disorganized.
In other words, you have no computer hardware or software issues you are trying to resolve (Aperture has no idea whether your organization works for you or not).
Instead of creating a new Library and then working with two Libraries, you might be better served by making your entire current organizational structure a child of a top-level Folder in your current Library. That way it is always available and capable of being hidden (use the disclosure triangle that accompanies every Folder to hide and show), and it remains both easy and frictionless to move your Images/Albums/Folders/Projects from the old structure to the new structure.
When you have completed building your new structure, there should be nothing left under the Folder you created for your old structure that you want to save. At that point, delete that top-level Folder. Voila! -- you have the new Library you want.
If your current Library organization is so much a mess that it is going to be easier to "start from scratch" (retaining, of course, all the adjusted Versions), then I suggest using Projects View (set to ungrouped, sorted by date ascending) to merge all your existing Projects into a series of large Projects based solely on date -- keep these to about 1,000 Images each -- and then in essence going through each of these "super-Projects" and breaking them into the Projects that should have been set up all along, viz.: Shoots. Once you have re-sorted all of your Images into new, consecutive, shoot-based Projects, the rest of your Library organization should be much easier.
You can accomplish the same thing, more simply, in Photos View (sort by date ascending; select consecutive Images, "File→New→Project" with "include selected" checked). The users I've worked with have been more comfortable seeing their existing Projects (in Projects View) rather than really starting fresh with every Image in Photos View.
Two notes:
- This is based on first creating a sensible and consistant Project-based grouping of your Images.
- Your Images contain the adjustments needed to make them. Nothing here changes that. All you are doing is changing the containers that hold your Images. (If the Image is table-setting, you are putting down a new table-cloth, and centerpiece, and table, and building a new dining salon, and castle, and grounds -- without changing the table-setting at all.)
This is complicated, but doesn't endanger your data (and, of course, you DO have a backup, right?). Post back with any questions.
