Hi Kristen and your colleague,
Here is our experience for IBM Maximo testing with our clients.
Where we start - found it has been really useful to have a living document written in business language that describes the core business critical functionality - both base functionality and configuration (and definitely any customization!). Set this up in Excel by functional area with a lead user + Maximo analyst who own. Starting point for defining your test cases and focusing your testing (and reference for training materials).
For fix packs - Maximo analyst should read the release notes to understand what is changing or being introduced. We have seen cases with clients where the 'fix' changed functionality that was actually working ok for the company. The 'fix' produced different results. Definitely less user testing effort for fixpacks - focus on what is changing or new.
For upgrades - Maximo analyst and business lead user should read the upgrade notes. I think it has worked really well with our clients to use the upgrade as an opportunity for 'whats new' or refresher training. For testing - test cases should cover the end to end business processes. Make sure they also cover user permissions, data restrictions, performance, screen UI layouts, data QA (all of which usually come through 100% clean - but the auditors often ask if these were verified during a systems upgrade). In terms of effort - would expect each functional area business lead user (not IT!) to spend 1-2 days initial testing after first pass of the upgrade. Then after second pass of upgrade another 2-5 days doing detail testing to get comfortable with the new version, identify any glitches, and note the changes in the UI or functionality that should be included in the refresher/ whats new training.
Hope this helps. Feel free to post with any specific questions or anything I have missed,
Richard