Well, since I’ve upgraded to Dorico 6 I can resume asking questions.
When I add objects such as Text or a Dynamic, Dorico increases the vertical space between staves or systems to accomodate them. But often, the new object is not well placed, so I switch to Engrave mode and move it. I expect that Dorico should automatically recover that vertical space, but it does not. I must over-ride the vertical spacing. Is there a better procedure?
Short example in the attached video.
I find that frustrating as well, but that’s just how the program works presently.
For Staff and System Text, you can turn off the Avoid collisions property. For other things like the dynamic here, you can often flip its ‘canonical’ position to above the staff, then manually move it back where you want it in Engrave mode.
After adding the dynamic, try flipping it to be above the staff then in Engrave mode move it back to where you want it to be. In this example it shouldn’t affect vertical spacing. If it does, enter the dynamic on the third beat then move in Engrave mode. The later method will affect playback but you could always go into the key editor and manually adjust the volume/velocity there.
The two very weird and unintuitive workarounds proposed by @hrnbouma both work.
(When I first started using Dorico last year, I resisted starting a Dorico How To document, hoping that maybe Dorico would be so intuitive that such a document would not be needed. Well, not including this current note, my Dorico How To document is now 5,760 words. My Finale How To note, which I developed over 20 years, is 10,113 words.)
Well, once you accept the fact that Engrave Mode edits do not change the spacing calculations,
becomes perfectly logical (and hopefully, second nature, dare I say: intuitive!), since it tells Dorico to not consider this object for vertical spacing.
I agree, @YourMusic.Pro. I wonder if the Dorico team has considered improving the program’s logic so that Engrave Mode edits would affect spacing calculations. I fear that the current logic is deeply embedded into the foundation of Dorico.
It certainly seems so. With respect to this behavior, I personally have indeed reached the acceptance stage… 
Maybe the question should be: How can I force Dorico to rerun the spacing algorithm after I have identified and corrected anomalous markings?
There’s no command for it I’m afraid. Dorico is designed to do it automatically all the time.