Omg I love this, this is the most interesting this forum has been since I joined hah
I'm just MJ eating popcorn here, but I would say this from my experience working with clients -
A non-destructive workflow ALWAYS ends up saving me more time than not. That's why I always render out EXRs with the largest amount of AOVs necessary for the job and just deal with the larger data-space and slightly slower preview times on AE.
Somehow, the client always ends up wanting to change some color, change some lighting, mask something out, blah blah. PNGs just don't hold enough information in them to do these changes in post well.
Re-rendering a project is always much more expensive and time consuming than working with EXRs. That's my 2 cents anyway. Carry on.