i dont think it would make much difference. djourou is easily one of the top 10 CBs in the league, and clichy, as poor as some of his game is, is still one of the 4-5 best LBs in the league.
our defensive problems start in midfield. just switching up the back four doesn't help us narrow passing angles, close passing lanes or track runners in the buildup.
though you're right in that maybe those signings, if experienced enough, might do some of the coaching that wenger isn't doing.