Spurred by Darren's latest nugget, I think it would be an excellent addition to the feature to be able to retain wire values for all subVIs of a particular VI as well as the VI itself. Several times, I have found myself having to run a VI a couple times to get to the point where I can satisfactorily examine the data flow. There is a JKI RCF plugin by Vishal posted herewhich implemented this, but native functionality would be much preferred.
I'm not sure how best it could be implemented in UI so as not to disturb those who don't want this, and I can forsee a hairy situation arising if a particular subVI is called from a different hierachy later. Ideally, the subVI would retain values for the last execution in the retained hierachy, but obviously that's incorrect in the grand scheme of things. I'd love to hear other ideas on how to handle that scenario.