I've grinded out a Large Cart mostly as a solo player, and if all you do is carry cargo it's a complete waste of time.
The Large Cart (which requires 3 REFINED Tier 3 planks (so you need 30 farming, cooking, masonry, forraging, carpentry and woodcutting to make)) still only holds 20 cargo slots (two stacks of 10).
Upgrading the carts only increase the inventory spaces.
What's the logic behind this? What incentive do I have to upgrade my cart past an improved cart if I only need it to carry cargo?