I disagree. Nothing I've seen of Sandro suggests we should be signing him. He's a rash defender who fails to do the basics. He's quick and can cover his mistakes but he seems to overplay a lot when in defensive positions.
Kolarov and Clichy are both below the level we need. The issue we have is that Kolarov is excellent at set pieces, will whip the ball in for the our strikers and can do a solid job defensively against most sides. Clichy is defensively sound, but doesn't offer much going forward but is homegrown. I wouldn't sell either player for Sandro, but I'd be happy to replace Kolarov if we signed someone with similar attacking instincts but that is better defensively. Moving forward we may be able to produce our own homegrown left back to replace Clichy.