FWIW, I have a lot of what you’ve described in terms of non-vivid sensory memories; the primary difference is that my factual memories (“I once did X”, without sensory context) are very important to me, and I don’t have the pain response.
Having said all of that, it may help you to know that my access to childhood memories has improved significantly after therapy, and this was not a therapy goal at all. If you are in the SF bay area, I would be ecstatic to recommend my therapist: http://mylesdownes.com/ (site looks much more newage then he ever behaved with me).
Of course, but I can help preserve the memories I choose by remembering them, reinforcing the connections. I dunno about Alzheimer’s, but with, say, CJD, anything could disappear at any time, reinforced or not. It’s not the same, to me.
-Robin