A large amount of stolen MtGox bitcoins appear to have been sold off at MtGox and other exchange markets, which would have somewhat pushed the bitcoin price down. However, since the coins were moved relatively slowly over time, and this was back before the bitcoin price exploded, the net monetary effect on the market may well have been pretty limited.

While a decent chunk of MtGox deposits were in a sense "fake" after all (that is, made using stolen funds), the net result for the creditors remains fairly unchanged; if the thieves deposited stolen coins onto MtGox, sold them for cash and then withdrew that money, we're still left with creditors who bought those coins for real money in good faith.

Notably, the fact that the coins were real, stolen and at significant risk of already having been spent would seem to further dim any hopes for creditors of recovering any more bitcoins. Realistically, we are left to hope the payout percentage might improve as invalid and illegitimate claims could potentially be filtered out.