I think it'd be great if stories utilising game mode could include random values in comparisons within text, as well as in chapter visibility/score changes. This would let stories really be more "Game" like! Currently I'm thinking of a random chance each day that the reader earns a promotion and better pay at work (which links to this suggestion), but there's probably an infinite number of possible uses for this.
I think that only creating random values isn't enough for most things, so that should always be on top of your other suggestion Game Mode enhancement: Add variables to each other. Also related the suggestion Formula Parser.
A simple version to use Random Numbers has been implemented for Score Changes. For the usage of the feature, see Creating Random Numbers.