One Neil Walker concern - has he always been so bad against left-handed pitching? His splits this season are ridiculous. .413 average, 1.187 OPS against RHP, .128 average, .526 OPS against LHP.
Walker's AAA splits, 2010:
vs LHP: .147/.237/.324 (.561 OPS in 34 ABs.
vs RHP: .404/.455/.697 (1.152 OPS) in 99 ABs.
Walker's AAA splits, 2009:
vs LHP: .228/.295/.370 (.665 OPS) in 127 ABs.
vs RHP: .273/.312/.523 (.835 OPS) in 256 ABs.
Walker's AAA splits, 2008:
vs LHP: .255/.285/.440 (.725 OPS) in 141 ABs.
vs RHP: .236/.278/.404 (.682 OPS) in 364 ABs.
I'd say that you have a sample-size problem, when trying to analyze Walker's "struggles" vs LHP in 2010, and that his splits versus LHP will even out to around the normal .700 OPS or so, given 125+ ABs against lefties.
Now, unfortunately, Walker's unsustainable .462 BABiP versus RHP in 2010 indicates that his RHP split is due for a southerly correction soon, as well.