We do re-create the top 15-20 best URLs by links of the former site in order to preserve the link juice. We keep these pages for search bots/crawlers and use them to insert links pointing to our most important money pages, internally.
We also tend to 301 redirect the remaining pages to relevant new ones should those be hard to re-build due to the unavailability of content or just not enough links that would justify building the whole page as opposed to just redirecting. So we re-create all pages that have a lot of incoming links and we 301 the remaining ones that aren't that strong to most relevant new buying guides.