When pre-sale investors (bought at $0.25~$1.5) withdraw and sell, maybe huge dump!

Interesting info. That works out to $0.94 average price. Without the first 2 tiers, the average price would be $2.66, still way below current price at EtherDelta.
Edit:
And in case you guys refer to the market depth of SALT to justify not selling, be informed that those who are sincerely out to sell will not quote anything in the order book, thus giving the false impression selling orders are thin.