It would be a disaster to start the season witih Zimmerman at first and Rendon at 3B. At best, like in the 10% world, that's a wash. Most likely its a loss of 2-3 wins. I don't see how you can project Zimmerman as more than a 4-win player at 1B based on his injury history, and I don't know how you project Rendon as more than a 2-win player. Before everyone goes crazy, remember than Zimmerman would lose 1.5 wins a season based on his positional adjustment at 1B as opposed to 3B.
There's no doubt about Tyler Moore being able to slug. When you carry a 250 ISO forward into the majors, that's never going to be a problem. Other teams are looking at him and seeing Mark Trumbo, and there's a lot more value in those kind of guys now that ISO has become scarcer and the offensive bar has been lowered a bit (average 2012 OPS 34 points lower than 2007). Look at how much more valuable LaRoche's output has become, just by being able to put up the same numbers in a different offensive environment.
It's hard to adjust your thinking, but most teams probably feel that a guy is a valuable commodity if he's under team control for 6 more years and probably has a floor of .250/.310/.480.
Personally, I'd like to see him get a shot in Toronto. He's a tailormade project for their "all ISO all the time" batting approach. I bet he'd hit 35 HRs there.