Currently, if you're unconcerned about morale levels, you only need to decrease taxes to up your morale for the turn of elections... which is a bit silly.

It seems pretty clear that the game logs morale levels, so why not use *that* for their voting preferences? That is, if they've been really unhappy for the past year, use that info -- don't let a sudden tax cut make them the happiest people in the universe willing to serve you. Could even weigh the past couple months more heavily.