I agree with the Home Sharing method (which I just learned about this past week). Here's how it works. Just enable Home Sharing on each computer. Then click on settings, (in Home Share) and enable new content to be transferred automatically to your computer. Then do the same on your wife's computer. Now, anytime your wife purchases content (and the new content ends up on her computer...either through an iPhone transfer or from purchasing directly with her computer), the content will get sent to your computer. The same will apply to her computer.
Since I have a large music library, I use the recently added playlist (set to two weeks), as a means to identify what is new and what isn't. If I like a song my wife purchased (which is in the recently added playlist), I just added to my personal playlists. You can setup a smart playlist like this to suit your family's needs.
Pros:
* You'll have a dual back-up of iTunes content (your computer & your wife's).
* You can do a TM backups and have 3 backups
* If something happens to either computer, you can easily drag and drop content from one computer to the next (via Home Sharing...even over WiFi).
* No need to worry about your server crashing...which effects both of you.
* With a WiFi already running, no additional cost & super easy to set up.
* If you stream to ATV, you'll have all the content on each computer in case its needed.
Cons:
* You both must have iTunes opened up on each computer at the same time for Home Sharing to detect and transfer new content to each computer.
* If you purchase content on your iPhone, you must transfer to your computer, then do the step above.
* Less portable in terms of taking your library to another computer at work, etc.
* Requires a bit more management to ensure you share similar likes. In other words, if you purchase something your wife would like, best to remember to tell her so she can look for it when your Home Sharing transfers your content. Could be hard to recognize new stuff from one computer to the next (of course, this would be a con for any setup).
In my house, we have 3 Laptops (mine, my wife's and my daughters) and a desktop computer. We have 3 iPhones. We all share the same AppleID. Therefore, we have a very wide range of tastes represented in all are libraries. However, I don't mind having my daughters content in my library because it acts a second backup in case something happens to her computer, etc.
I'd give it a try since there is no up front cost and see if you like it...I sure do!
Cosmo