The team built itself around Lester Buchholz, and to a lesser extent, Lackey. There is no getting rid of them, no matter what negatives you want to throw, they're here to stay, and there aren't better replacements available within ruining the farm.
The next two spots however, can make a very big difference to the team if they pull in a guy like Peavy or Johnson with a big trade, and then sign one of the mid-tier #3 type pitchers available in free agency. Picking up a #3 would slot the team like so:
Josh Johnson
Clay Buchholz
Marcum
Lester
Lackey
Buccholz has been very impressive the second half of the year. Lester as a #4 is pretty sweet, especially with his upside. And even if Lackey falls apart, they can fill the spot with someone like Aceves, Morales, Tazawa or any of the other options on the team who could possibly be a solid fifth guy-- pieces who you know will never pitch for you in the playoffs.