I've just figured out what has been making Diagon look slightly odd to me. The buildings are excellent, but I couldn't work out why it still looked a bit different to the films. Turns out it's the lack of street furniture and clutter. I understand it's pretty much impossible from a H&S point of view, but that is the one feature which gives Diagon it's character I think. In the reveal scene in Philosopher's Stone, the street is covered in stalls, carts, crates and cages; hopefully a couple of street sellers or Magic Neep-style stalls will turn up in due course.
I wouldn't rule this out; that kind of stuff wouldn't be installed yet. I don't think it will have items all over, but I bet we're going to see a lot of what you're looking for. POE would be a good example. Props can be installed last minute.