To be fair, Iglesias is hitting .270 with a .321 OBP as of right now. Those are far from spectacular numbers, but if he can take a walk, move runners over, make productive outs, and get on base with a few bunts and bleeders, his defense will make him a very valuable player.
Ozzie Smith had a 4.2 WAR with a .589 OPS in 1981.
To put that into context, Hanley Ramirez had a 4.6 WAR in 2010 when he hit .300/.378/.475 with 21 HR, 76 RBI, and 32 SB. But his defense was atrocious.
Defense up the middle is absolutely critical. If we can get a .230-.250 average with a .290-.310 OBP from Iglesias, we'll have a very productive SS.