Some stats:
If I won the most common prizes (highest %) on map 1, I would get:
30 Diamonds
12 1hr instants
3 2hr instants
2000 Fragments
3 Catalysts
1 5% Portal Profit
4 coin/supply instants
If I won the rarest prizes (lowest %) on map 1, I would get:
20 catalysts
12,000 Fragments
1 10% Portal Profit
1 building
1 building or 75 Diamonds (same %)
1 building or 100 Diamonds (same %)
By the way... most of us REQUESTED that coin rain and supply windfalls be removed as prizes in the Spire... there are 8 of each as prizes on map 1.
So from this data, I believe that the Spire was created to help us gain the necessary ingredients to CRAFT in the Magic Academy. So we are trading troops for necessary AW ingredients, necessary ingredients to upgrade buildings, spells, and KP or we are trading troops for crafting ingredients, rare buildings, and a few other random items in the Spire.
If I have to choose between the Tournaments or the Spire, due to troop limits, it will definitely be the Tournament until all my AWs are at their highest levels.