I redesigned mine a couple of months ago and am getting much better search engine places (other than google as in the sandbox still). I kept pretty much the same content but expanded on it a bit and added new stuff. I think as long as you keep the search engines in mind when doing the redesign and keep pretty much the same or more content you shouldn’t see a problem. Remember to keep the same filenames as before if certain keywords go to certain pages.
Arn