I don’t know that consolidation is about the reduction of identical applications or systems so much as it is about the consolidation of redundant “types” of applications or systems.
Solving this problem is the same problem that people in charge of Mergers are dealing with. In a Merger of two enterprises, you almost immediately run into redundancy of systems or applications but the technologies used to implement the same types of solutions may be very different.
The strategy used by successful Merger professionals is as follows…
1) Itemize and prioritize all unique IT Disciplines. This gives you a linear list of all major functions performed by an enterprise.
2) Associate all Systems or Applications that exist to their correlating IT Discipline. This shows you clear purpose of the Application or System. Also, as you relate each to its correlating IT Discipline, you will be able to clearly identify redundancies.
3) Associate Costs to each System or Application (Delivery Costs, Maintenance Costs, Headcount Costs, etc.). This will allow you to help develop the ROI of consolidation for each Application or System in each IT Discipline area.
4) Develop the ROI for consolidation. This should not only include the Savings but should also include the Investment Cost to Disinvest and a clear Break Even Point.
I hope this helps.