Dear Julius/Sergio
Thanks for the valuable comments. The upgrade in our case has been done including the regression testing.
One of the scenario where we had the big issue was related to batch master. One of the custom report which was related to batches creation and was using function module VB_CREATE_BATCH had added a new authorization check at a very deep rooted level. During testing of this in quality the Functional Expert had more authorization so no issue was reported
But sadly the moment it went live it affected everything.
I am sorry but i did not understand how SU22/SU24/SU25 etc. would have helped in such scenario( please bear with my limited knowledge related to Secuirty 
)?
Seconldy I am thinking purely from a developer point of view, do we have tool which clearly highlights even if we missed in testing, that so and so tcodes/reports are impacted?
Thanks
Nabheet