On the 380 FB group we sort of have discussed this topic. I agree that there isn't enough storage in the galley, salon. One suggestion is to build cabinets over the stove area. All new lagoons have these, and there are some pics from an ex 380 owner who did this. I am looking at cutting out a door to the right of the fridge when looking at the fridge. Normally this space is accessed from the owners cabin behind the sliding door. I find that there is enough room in the owners cabin but this would be better used in the salon.

There is tons of space under the seats in the salon but I agree it is very hard to get to. Besides what you said, my typical rule in sailing is that whatever you want to do, there is always someone right there you need to ask to move. Someone is comfortable in the cockpit, you want to move the traveller, etc.