Overall, it's hard to tell via a computer monitor. Since they added the silver corner plate and it was a not an original feature, I'd have to say that the saddle was not on Circle Y's upper end.
That said, I own a Circle Y myself and really like it. Well made and very comfortable. Based on what you know about it (age does play a factor as well) I wouldn't pay $1,200 for it.
It's a good idea to look around and see what comparible saddles are selling for in order to get an idea on a fair price for this one. Personally, I'd probably offer somewhere in the ballpark of $850.00 and see what they say.
Good luck on the purchase of the mare.