What about using the CMS functions of vBulletin? I know of people doing that with great success and it would keep your changes to a minimum.
I would say this is not something to fiddle with trivially: "I have been on page 1 of Google for 9 of those years" Kudos!
Personally, I would, however, say this is a myth: "I ranked so well for so many years because every bit of my code on the core pages, was 100% unique and hand written from scratch. "
So balancing those two considerations, I would want to be very careful about rolling things out and try to keep the static pages as close to the original as possible as you integrate them into a CMS if you do at all. You might find that with a little bit of scripting you can pull some dynamic elements onto those pages and keep thems eparate from the CMS.