Two other thoughts on this...here's the approach I would take...
1) Go back and update just the posts over the past couple of years, as well as key trip reports. Let the older stuff go. Yah, it's painful. I assume you know how to find all posts you've written via the vBulletin profile tool.
2) Update your sig to include a pointer to where all of your photos are now. So if anyone runs across a missing image and are really curious, they can look it up via your web site. Your option whether to include an editorial message around your photo migration.