The Mets should use either Kirk Nieuwenhuis or Matt Den Dekker as their forth outfielder. Nieuwenhuis is probably more major league ready at this point. The value of the Mets forth outfielder is huge for this team and will provide the opportunity for a lot of playing time. Andres Torres will get a full shot at being the Mets regular center fielder, but it will be nice to know that there is another option outside of Scott Hairston. Hairston is a nice PH threat but should not be an injury away from playing every day. Lucas Duda is in his first full season for the Mets and there are still serious concerns over what Jason Bay has left. Duda played very well last season and may be the smallest question among the three outfielders.
Using either Nieuwenhuis or Den Dekker on the major league roster to start the season will interest fans a little more and give them a chance to see some of the younger players the organization has been developing. I agree that neither should be projected to be a star, but they both become useful players. I can see either becoming getting the equivalent of a full season replacing all three outfielders. At this point, it will be a more productive move than adding a Corey Patterson or Rick Ankiel.
As for backing up the Mets infielders, I am forced to accept Ronny Cedeno as a part of this team's bench. I still see no use in clogging up a valuable spot on a bench that will need to be used more than most on a player just because he knows how to play shortstop. He does nothing else. I like Justin Turner, but it may make sense for the Mets to trade him at this point. Staying along the lines of Nieuwenhuis and Den Dekker, I have considered suggesting the Mets using Reese Havens or Jordany Valdespin as bench players to start the season. I don't feel as strongly as I do the outfielders, being this spot could be better suited for a super-utility player. Valdespin has played one year at SS, and Havens would be better getting the chance to play every day in Buffalo. Havens will play every day at 2B if anything happens to Daniel Murphy.
I like the versatility of Ryan Theriot and Aaron Miles and wonder if they could possibly fall into the Mets lap. Otherwise, I think the Mets should consider a trade for a Joe McEwing like player. The emphasis has to be second base with the ability to play other positions. Robert Andino could be a fit from Baltimore, perhaps Mike Fontenot from the Giants. Other trade options could be Sean Rodriguez from the Rays, (you would have to give up a prospect for him) Don Kelly from the Tigers and Brandon Ryan of the Mariners. Perhaps even Wilson Valdez could be pried from the Phillies. They would all make the Mets bench deeper than it is right now.