I posted a thread on this about a year ago. I even posted a picture of my mirror surface. Sonds like your mirror looks just like mine or maybe i should say mine did.
As I understand it, you can get the mirror glass only. The mirror glass with Auto Dimming option is not cheap. Something like $300.00 US dollars. The mirror glass is very easy to change out no matter what feature or option you have. Just follow the instructions per this sites link: http://www.wjjeeps.com/mirrors2.htm
Somewhere within that link, you will find pricing for the mirror glass if you want to go that route.
I spent some time "junkin" as they say. I found a 2002 with a good drivers side mirror glass which had the heater, but not the dimming feature. I have already installed that mirror which again was very easy.
I bought my 2004 Overland used and the mirror was already like what you described. I think the feature would still work if I had a good mirror glass, but that would be the question for you. If the feature does still work, you wouldn't be wasting your money buying a new one only to find out there is something wrong with the system that makes all that work. It is a nice feature and a shame Jeep wants so much for the part. To me that is a reflection on Jeep as I have always felt if we can keep our Jeeps looking and running good, that is pretty impressive to the public and future buyers. Is that not what it's all about!
Anyway, good luck and thanks for contributing to a great forum for us Jeep lovers.