I too enjoyed Quantum of Solace better on the second viewing and soon after watching it's prequel on DVD. I think it's a good film, not as good as Casino Royale. As for your plot hole, check out this extra scene.

M: We're going to send Caruthers with the money.
Mitchell: Excuse me, M.
M: Yes, Mitchell.
Mitchell: Caruthers? He... er, drinks, so sending him to a Casino would be a mistake.
M: You're over-stepping your role as my body-guard.
Mitchell: Sorry, Ma'am. I just notice things-
M: That's all right. Who would you suggest then?
Mitchell: There's Vesper Lynd.
M: A woman! You know what Bond's like.
Mitchell: She looks like the back end of a bus.
M: Very well then.