I have a mermaid room and the mermaid exterior. I find its really hard to get cute exterior house items that appeal to me so I don't see a reason to change it. I am also trying to get the full mermaid set inside before I sell it. I love the set but I understand why people don't like it. I think its just the wall and flooring that rubs people the wrong way.
My other rooms has a tropical theme, a regal theme with instruments, one apartment style, and the last I am hoping to change it to a cafe with roosters items.
I try to keep everything neat and purposefully set up and I'm really proud of it. I don't think having the same set is bad as long as you put it nicely with other things. Lastly, I do invite you guys to come and see my house via the dream suite and tell me what you think. 
