I think it might be interesting if:

1. You can only play the daily challenge once.

2. different settings. sometimes reveal map. sometimes majority buy out, and so forth. (in addition to the earlier suggestions) 

3. a high scores table for each daily listed by in-game time it took to win (with a second sort of stock price in case of ties, and for unfortunate losses)

edit: Maybe be able to play daily challenge more than once, but only the first time counts for the score board.

also, if the settings are variable, it would probably be beneficial to be able to see the settings before the game start... maybe. not sure about this.