There has always been much debate about the value of work and time required to understand the current system and/or process before expending effort (resources) to define the requirements for a new system. Play the role of a project/requirements manager and justify to your customers/superiors the reasons to budget time and money to do "as-is" analysis. Explain how it can be beneficial, in what situations it is necessary, how it can more than pay for itself by saving costs and time in the long run.