The entire glamour system is a mess

[Laraul]

From what I understand they sync your entire inventory with the server every few seconds - even if you are just walking around with the inventory closed.
This means that any increase in inventory space will result in increased server load.

You understand incorrectly. The game retrieves your inventory from the server every time you enter a zone. I know this because I once had an soul crystal "disappear" from my local inventory when swapping between two gear sets too quickly. I was able to restore my inventory by simply teleporting back into the same zone I was in.