Most of the struggling secondary players are at least contributing with their gloves and accumulating positive WAR. Gimenez, Kirk, Roden and Clement are all putting up positive WAR despite their bats being cold.
I don't think a couple of no defense, 20+ homer types (aka the kind of Free Agent pickups that this board clamors for) would be providing much more value than they are.
The one guy who is really sucking big time is Will Wagner. He's a negative on defense so needs to hit but he's not at all. His projections are so good I'd keep playing him but 3B is the most obvious spot to improve at the trade deadline right now.