Sc00byUK I think it is a long time investment, it will pay itself back, but it will take time.
I bought the museum originally when I realized that I would get most of the coins back from an achievement if I placed 5 ships in the museum.
So far I have only upgraded it twice At the end of the Greek and Twain events as I needed xp to be able to buy the Anchiocus/Hornets...
I will soon have 4 more ships ready for the museum, so I may consider upgrading it again soon.
If I had upgraded it more earlier I might have earned it back by now, but it is usually my lowest priority.
Edited: I get 544 coins per hour for a full level 3 museum, so if you only get 4500 coins per hour for a full level 17 museum, then it looks like it will take a long time to earn the investment back, especially if you buy and upgrade ships only to put into the museum😢