A tiny bit of it is or was on display in the museum, by the stairs to the art gallery. There is enough of it in storage to be able to restore much of the layout, but the rolling stock etc has suffered. Unfortunately, people know the value of the thing and quite a bit of it was stolen in the years before the museum existed, or had the means to securely store it. I am told that people - collectors - borrowed locos etc on the pretext of fixing them, and never brought them back.
I believe it is regarded as significant because manufacturers - might have been Hornby himself - "took inspiration" from the engineering.