It seems highly unlikely that nothing would be reusable across campaigns. Identifying the commonalities and isolating them into subprojects that you build out in small increments would seem to be a benefit.

In fact, I've been to a presentation by a digital agency on how they did exactly that and improved the time-to-launch on new projects as a result.

Besides, you don't want to overengineer anything. Refactoring will happen, so the design can be deliberately minimal at the start if proper refactoring practices can be applied.