Starting with Legacy Rules

At least 50% of our BR projects involve excavating "rules" from existing legacy code.  This does not mean simply chopping existing code into smaller pieces and forward engineering them into new technology. It usually means trying to salvage the true business rules out of the code, correlating them to business vocabulary, and analyzing them for business value prior to putting them into newer technology (such as a BRE).  At odds is that the mining of rules from code requires very technical resources while the analyzing of them for business value requires knowledgeable business leaders.  How have people addressed this challenge?  What kinds of people and skills are needed for a project that starts with mining rules from code, then analyzes them for business reasons, then forward engineers them into a BRE?  Do such projects often involve mining rules from code and from documents and from peoples' heads?  If so, how are these rules integrated safely into an automated solution that makes sense?  (We are finding that this is a requirement that is becoming extremely prevalent).