Your team is stacked, but unless there are two Jose Reyes in baseball, I think your missing a utility player
. In terms of trading, your biggest flaws are at Catcher and Relief Pitcher. Posada has jumped out to a great start, but I see him as a sell high candidate. Either try to sell him in a 2 for 1 special for an elite catcher (like the DL'd Mauer or Posey), or check the waiver wire for a potential backup (Avila or even Napoli in your league). At Relief, Lyon is on the DL and maybe out of his closing responsibilities for good. Are there any RP (even like his replacement Melancon) you can also snatch off of Waivers?
If you want to pick up Dunn, the obvious choice for me is Markakis. You have plenty of good OF, and Dunn could slip into Reyes utility spot (considering someone else isn't there). Of course Dunn, like newly acquired Morneau is only 1b eligible. Since Adrian will be your stater, Dunn and Morneau will likely compete to play utility. Therefore another option is to drop Morneau. I do think Dunn has more potential then Morneau, especially in categories for power.
Good Luck and I hope this was helpful.