Admittedly, Mark had a terrible year last year. He hit about what you'd expect. 37 HR's is never a bad thing, but of course he strikes out in bunches leaving his batting average low with the attendant lowish OBP (.323).
The thing that made his value barely above replacement was his fielding. According to Fangraphs he gave up almost 3 wins with his glove. Of course this is terrible, but the next worse years were minus one win. That's still not good, but it's not The Exorcist level horror of -3 wins.
Based on past performance and the fact he's still fairly young (29) a reasonable projection would be about 2 wins. He hits bombs, isn't a disaster on the OBP front, is durable, and plays poor defense at third. The total package (which is all that matters) is positive.
The incumbent, Donaldson doesn't hit bombs, may not even get on base at a decent clip, and so far plays poor defense although there's some hope there. The chance that Donaldson makes it to even a modest 2 wins is remote.
Mark is the perfect stopgap. He's owed 7.5 million this year with an option for 11 million in 2011. At 7.5 mil there's a little surplus value so he's worth trading for assuming a win is worth about 4-5 million. 11 mill for 2013 is over priced, but the A's just decline the option.
The other bonus is the circus atmosphere that Mark will contribute along with Manny and Yoenis. A's: Sometimes awful, but never boring.
The question is: Should the A's pursue Mark as their starting third baseman?