Best methodology for application effectiveness assessments?

Post IT reorg, my new postion is Quality Assurance Analyst (from BSA). My main job is to do after-the-fact application effectiveness assessments, on our existing systems like our Siebel & event mgmt systems, financial package, etc. We're looking at high level value to the business (is it aligned with our business strategy) to low level business process/product assessment and improvement (does the zip code look up work). I'm working on creating a methodology at the detailed task list level based on the best of COBIT, balanced scorecard, & ITIL. These concepts are brand new to me. I can't find much help out there except where it applies project QA or QA during the engineering phase, which doesn't help. Any suggestions?