Well, for one thing, Iglesias is going to see an inevitable huge slump soon. His BABIP is over .500. So while he's capable, Bogaerts would be an upgrade by August.
And Drew is fine, he's playing well, but if you've got a guy who can provide as good or better production than him, you don't hold him back for a player on a 1 year deal. You get what you can get for Drew on the market if Bogaerts is forcing his way on the scene.
The upside that Bogaerts brings is insanely higher than Drew, and if he is having the same success in AAA as he's having in AA, you absolutely trade Drew and promote Bogaerts.
Just look at Middlebrooks last year. Same situation. Youkilis wasn't hurt anymore, and Middlebrooks forced his way on the scene.