In a way, I agree with you here. With their first two LPs clocking in at 11 tracks, they found a really good album construct. X&Y is plagued by some, for lack of a better word, abysmal cuts, but reconstructed with some of the better non-album X&Y songs, it would have made a good 11 track album (although still not up to the excellent standards of Parachutes and Rush).
However, I can't really say whether or not 9 tracks would be a huge problem. Sometimes brevity can be a good thing. My favorite album of 2007, Okkervil River's The Stage Names, clocks in with its nine tracks at about the mid-40's mark. A seemingly stingy tracklist resulted in a terrific album, so I can't say whether or not a similar approach from Coldplay would be a bad thing. Honestly, it could be just what they need.