What about use for weddings? Sort the gardens out and it would be a lovely venue.
You'd get enough for a wedding, but not a large wedding. You'd maybe be able to get a congregation of 50, so suitable in some circumstances.
But like Rob says, they'd need to sort out the Gardens first, you'd be paying a premium for the view, and at the moment the view is a little... neglected.
I would have thought that main room has a reasonable capacity to it. Given that, I believe it was the entire space dedicated to the restaurant during that era.
I don't think it was much smaller than the space my venue used to use for 70 person weddings (and even then I think our capacity was set by fire restrictions, rather than the number of seats we could have accommodated.)