I originally summarized my thoughts here: http://angelswinblog.blogspot.com/2013/09/strategic-reload.html
However, I think Trumbo and Kendrick are the two most likely targets to be traded rather than Bourjos or Aybar and I think it is absolutely necessary to acquire the pitching depth a team needs to make it through an entire season.
Trumbo doesn't really have a position to play regularly with Hamilton in RF and Pujols at 1B. On top of that Calhoun can support both of those positions making Mark a potentially tradeable piece. He has value in a market that is looking for corner OF and 1B power bats. I like Mark and you can't easily replace his power but he would, in my opinion, bring in a young, cost-controlled top of the rotation pitcher.
Kendrick has a bit more value than Trumbo. With Howie we have players like Green, Lindsey, Field, et. al. who can potentially replace his position. Kendrick could net us a young top of the line starter and a relief pitcher (or another piece like a 3B). Again Howie does well on offense and is above average on defense but the "downgrade" to one of the other options is more than made up by the upgrade to our pitching staff, making Howie expendable if we have to move him.
Aybar to me is less likely to be traded simply because we don't have good options (Field and Romine) to take his place. Erick would bring back a Kendrick-like return in trade but it seems less likely at this moment in time.
As far as Bourjos is concerned I think we would be selling low on him and Dipoto has stated that he believes Peter will be in an Angels uniform at least through his club-controlled years. People call him injury-prone but only his hamstring issue was "self-inflicted", while the other injury was caused by an errant pitch. I think he stays unless the Angels get a really good offer for him.
I think Iannetta might go too if Dipoto can find a taker for him. His defense is lacking and his only main offensive ability is his OBP and the occasional long ball.
In the end I think the Angels will pursue Tanaka and try to resign Vargas. If they do both I still think they will deal Trumbo and/or Kendrick, first, and Aybar and/or Bourjos, second, for additional pitching depth. Most teams want to be at least 8-9 quality pitchers deep in the rotation, i.e. no scrubs, only real talented pitchers.