"I wish Apple had a solution where you could download the update once then redistribute it."
They do. Two in fact. Once it's on your own network, use Caching Server inside OS X Server. $20. Worth the savings in aspirin alone. Or ARD. Similarly cheap.
Outside of Apple, sneakernet. Store apps like XCode only care that you bought them and they they are intact on the drive. I did this for several large in-the-store, non-installer-based, free-with-OSX apps (GarageBand, iMovie) in a building that shared a 10-base fiber link across 18 machine and I wanted to get home for dinner.