According to DC United, they're looking for an impact player in this year's Superdraft. It rare, however, that find such a player coming out of college. I argue that the true impact players are either players who have gained a few years professional experience outside of college, or they are signed from other parts of the world. The biggest impact player from last season, Andy Najar, was signed from the team's youth academy. It can be argued Tim Ream and Danny Mwanaga were impact players for their respective teams. However, it truly depends on how one defines impact player. To me these players have filled in holes that each team had and were valuable pieces to the team's puzzle. I classify impact as David Ferreria in Dallas or Omar Cummings in Colorado. Neither of these teams could have made the MLS Cup final with out the contribution of these players. Therefore, impact to me is dictated by the final results at the end of the season.
I don't think DC can find an impact player in the draft, until he is atleast developed in the league for a few seasons. However, they can find a valuable piece to plug into a terrible team.