Just curious, what kind of items are you finding before you reach level 40 in such quantity that would make a 24 slot vault more useful?
I'll give you 2 scenarios, both of which have happened in the last 3 days, and then a 3rd scenario that descibes people who play the game differently from me.
Scenario 1: Each time the civs level up
The specific scenario yesterday, that lead to making this suggestion, was when my civs (all 6 of them) hit level 21 and so I was crafting new gear for all of them.
Lvl 21 Superior Water Bags - Craftsman x10
Lvl 21 Majestic Holy Staff - Religion x8
+ 2 other items, Lvl 21, 1 each
Right there on the spot that took up 20 slots, which meant that I had to unload the materials that I usually keep in the vault so I could use the vault to move the gear to my civs, and then go back and pick up the materials after I was done.
Obviously some of the civ-switching is going to happen no matter what, and is not related to vault size. First I had to go to my Egyptians (my Religion crafter) to make a sample Majestic Holy Staff, then to my Celts (my Craftsman crafter) to make a sample Superior WaterBag, then I had to check all 6 civs to see how many of each item I wanted to make for each civs. Now that part of the work would be necessary no matter what, that was 7 total civ switches to gather information before any crafting is done, then 2 more civ switches to go back to the crafting civs and make up all of the items.
But the extra civ switching that was needed in order to empty my vault so that I could move the 20 items around, and then go back and recover the materials that I like to keep in the vault, could have been removed if the vault started with a default size of 48 slots.
This scenario happens every time the civs hit a new level starting at about Lvl 15, when I started paying attention to gear. For levels 15-20 this only required swapping between the three starter civs, Celt, Greek & Egyptian, but with Lvl 21 it involved all 6 civs, which means it's going to happen 19 more times on the road to hitting Lvl 40.
Scenario 2: During the leveling process
This one happens a big more often, as it's fairly normal to start accumulating items that other civs can use.
As I said, I keep all of my civs in sync. So I'll start by playing the Celts, as I play scenarios to get them up a level some items start to accumulate in the vault for other civs.
Then when they hit the next level I move on to the Greeks. I may or may not get to pull items from the vault for the Greeks, but then items begin to accumulate in the vault for the other civs.
Rinse and repeat for all the civs, and before you know it you have a full vault and you have to start swapping to other civs just to clear out vault space.
Scenario 3: People who play 1 civ at a time all the way to Lvl 40.
When I first played the game, back in the Microsoft days, this was the plan I thought I was going to follow and, I suspect, it's a pretty good description of most people who have never played the game before and have only discovered the new incarnation from word-of-mouth.
The problem is that you very rapidly built up inventory for other civs, and when you're playing just one civ at a time you can rapidly fill the vault and then still overwhelm your own ability to have enough storehouses to hold all of those items before you play the other civs.
Back in the day, when this was a Microsoft game and I was new, I was basically forced to spend some time leveling the Celts and Egyptians for the sole purpose of getting some storehouses for those civs, just to hold all of the extra gear for them. I also used them to store gear from Lvl 21-40 for the Persians, Norse & Babylonians until I unlocked those premium civs.
While it's obvious that 48 slots is not going to completely fix this issue for a single-civ player, it's still a significant improvement over the default 24, a number that was deliberately kept low by Microsoft because they were trying to use Vault space one of the components of their revenue model.
tl;dr
Having said the above, it's clear that none of these scenarios are earth shattering, no one is going to quite the game because of vault inventory, players will make adjustments based on the available spaces, this is ultimately a "quality of life" suggestion. Since this is not a for-profit game, and there's no desire/intent to generate revenue by artificially limiting vault space, I think it makes sense that the base vault size would benefit from being substantially larger.
I'm basically working from the same logic as the decision to have all 6 civs unlocked right from the beginning. In this new Celeste incarnation of the game there's no such thing as Premium Content, and I think that a larger default vault size matches the spirit of unlocking all 6 civs by default.
greetz.