Your truck, your money, your mods
But since you asked my opinion.....hehe....you'll love the airaid intake, and the TB spacer won't do anything (but if you install at same time you won't know the difference...)
I'll even explain my reasoning
they have to design for many circumstances (off roading, daily driving, etc....) so the intake has to be suitable for all things (same for what you mentioned about the SC or Diablo....can't have a factory performance tune and not be able to tow, it is a truck). As for the TB spacer, can't see any instance that they would design for without it, so if it was beneficial they would probably add it.
Anyway good mods, your choice