Ok, all. I think I found the problem. In searching for reports of this issue and solutions I found someone that mentioned they had fixed a similar issue with a "free" program called "iPhoto Library Manager." The app apparently lets you split a library into multiple smaller ones or combine multiple libraries. Generally it just "manages" your libraries. I figured I had nothing to lose so I checked it out. Turns out it costs $19.99 but they do have a free demo.
I launched it and it immediately told me that it couldn't display my library and albums due to an issue with the AlbumData.xml file on line 22155. I read in the documentation of the app under it's "Help" menu that likely causes were a keyword with a "null" character at the end, or a file path being referenced inside the library that had an ampersand or backslash in it. The person on the board I'd found had had a keyword issue.
Anyway, I opened the iPhoto library by showing package contents (right click the file to choose this) and loaded up the AlbumData.xml file in TextWrangler, since that displays line numbers. I found that line 22155 indeed referenced an mp3 in my iTunes library that had an ampersand in it. Deleted that line. Then it said line 22156 had an issue so I deleted that, at which point iPhoto Library Manager instantly displayed all my albums. I checked iTunes and it too now showed my albums and the option to sync only selected albums was no longer grayed out!
Per the Library Manager's instructions, I saved the AlbumData.xml file I'd modified. The app said the iPhoto only writes this file out, it doesn't read it. However, other apps read it to get your album info, hence the issue. So I had to go into iPhoto and fix the problem, else the next time I exited the app, it would write the file back out improperly. I noticed in the xml file that where the song was listed it was also referencing one of my albums. So when I launched iPhoto, I went to that album and checked the slide show settings. Sure enough, I had set a custom playlist for that album and listed the song I had seen on line 22155 in the AlbumData.xml file. I removed that song from the settings, and exited iPhoto. No more issues! I appear to be all set!
Now, I'm not clear if I NEEDED to edit the AlbumData.xml file. Just looking at it showed the error and then I had to fix it in iPhoto. So you can probably do that. However, the iPhoto Library Manager software is the only thing I know of that could show WHERE the error was. Since the free demo works for this purpose, I'd suggest giving it a shot. This issue is obviously caused by our individual libraries and is not an Apple issue. Now, the album that had the problem has existed for almost 3 years and I've never had an issue like this arise before so it's anyone's guess as to why it became a problem now. Fortunately, it's all in the past for me now, though!
Hope this helps someone. Good luck!
