I have built Dio's for years, but as of yet i don't have Shep's book. I always keep my dio's on the simple side. I have one, maybe two, main subjects, i.e. an aircrfat or piece of armour. I use everything else to tell the story and suypport the main object. The armour i build is 1/35th, so i don't do large battle scenes, but you can still show a vehicle in action. For aircraft i build 1/72nd, and the vehicles in such a dio would be to support it. But i personally wouldn't mix armour with aircraft unless the aircraft was a transporter.
I am not keen on the massive Diorama's with lots going on. The purpose of my Dio's is to show the vehicle or aircraft in a natural enviromet.