What are you planning on using them for? Where they were dropped yesterday, if you recreate the old site now I think Google will just see that as a lapse in judgement by the owner. These are great for building a network of domains linking to you (although none of those have a great backlink profile or PR for that). If you plan on stripping the site and building a site around your favorite diet product (or whatever) Google will see it as a new site, but the original age will still show in SEQuake and other tools. If you recreate the site, it will only count as being from 1996 if it has been the same site since 1996. If the site has changed hands a dozen times since then and you recreate the latest site you will have the age of the latest site.