The following are my best guesses...
Here's where I feel some natural regression is inevitable. Reddick does have some legitimate power, especially on the ball down and in, but he does not come across to me as a "true 30 HR hitter". Those are usually hitters who either hit the ball out to all fields, or who are primarily up there swinging for the fences as the main part of their game.
Reddick is a batter who has a "happy zone" for power (no I will not refer to it as his "honey hole"), and who can punish mistakes, but I would expect him to hit closer to 22-24 HRs next season -- which is just fine, but is also a sharp drop off from 32.
I think Reddick is capable of hitting for a higher batting average next year than the .242 he settled for in 2012. Reddick's .242 was mostly the by-product of his extended slumps. Cut the time of those slumps in half, as I think he can with another year's experience under his belt, and hit a bit more consistently to all fields, and I could easily see Reddick batting .265-.270, even factoring in the Coliseum's effect on hitting.
On Base Percentage
Don't look for a big jump in OBP from Reddick, outside of the boost it will get if he mixes in a few more hits. Reddick's plate discipline was a big issue in the minor leagues: Did you know that Reddick's career AAA OBP was only .300, his career AA OBP just .332?
The over-eager Reddick we saw a lot of last season, the one who would bail out the pitcher by hacking at "pitcher's pitches" on 3-1, and could be swayed to chase 0-2 pitches from head to toe? That's Josh. I suspect that of all the parts of his game, the one that will hold him back the most, over time, is his plate discipline.
I think Reddick can maintain a pretty solid slugging percentage, adding plenty of doubles to his collection of hits. Though he tends to pull the ball a lot, I think he is capable of hitting gap to gap and will develop that part of his game. I could even see his 2Bs total (29 this past season) creeping up into the 30s as his HR total regresses into the 20s.
This was a huge issue for Reddick, who batted just .206/.292/.394 with RISP in 2012. It's not that I think it was totally "statistical noise," because I suspect it got into his head after a while and caused him to press or try to hard -- do you get the feeling Josh is wound a bit tight sometimes? -- but I think that as part of the natural maturing process, Reddick will settle down and hit just fine with RISP.
In other words, it may not have been "just noise" last year but I think any variation will be going forward. I don't expect him to hit much differently, over time, with or without RISP and I still think he is best suited to batting #5-#6 rather than ahead of the A's best hitters. You want a high OBP guy in front of Cespedes, Carter, Moss, and I think that beginning in 2013 Reddick will be a good "RBI guy," i.e., a guy who doesn't get on base a ton but who is great to have up with runners on base because he gets a lot of hits, many of them XBHs.
It's for real. Reddick is one the best RFers in the game and I don't expect that to change. Even when he was slumping something fierce, he continued to provide value to the A's by playing excellent defense.
So what I might expect from Reddick going forward, with a full season now under his belt, is something like a slash line of .267/.332/.450 with 23 HRs, 32 2Bs, and "plus" COFer defense. You know who that sounds a LOT like? Ironically, he of the "why did we trade him???" lament, Carlos Gonzalez.