I have found out a couple things recently in regards to this.
First, yes having a t206 player autograph makes it a little more desireable. However, after a certain price range, only unless there is a collector out there DYING to get it, the value doesn't seem to be much there after $200 unless it was someone who died before 1930 and/or a hall of famer.
My reasoning behind this came from this Dick Egan signed payroll check I had.
http://www.ebay.com/itm/-/1915718306...EOISSA:US:1123
Egan died in 1947 and is probably at about the same rarity level as Atz. Now it being on a Reds payroll check should put it at more value then something just signed on a piece of paper or non baseball related document.
I started it at $199 and literally got one bid much to my surprise. Of course this could just be a fluke or bad timing.
There has been two John Titus autographs on ebay at highish prices (495 and 795 I think) and have been there awhile. Up til last year Titus was so tough even SABR didnt have an example of him for their deadball stars books. This year somehow 4 popped up. My guess is that the value on Titus has dropped dramatically even though his t206 is (or atleast was) pretty popular.
So my assumption would be, based on what I have seen this year, that a nice Atz autographed would go for between 200-400 depending on who is out there needing one badly. I have a few equally tough Cubs commons I am looking for but if they popped up now Imnot sure Id go much over 200 for them.
This is all just an opinion but hope it helps