I've been thinking that a possible gameplay mechanic for the Proposals and their voting would be to a two-part phase:
Phase 1: Put your proposal tokens on one or more slots on a d8. You've got eight slots, each corresponding to a different result for the roll of a d8 - You're basically betting on specific results or sets thereof. Perhaps you spread your proposal tokens on a whole bunch of faces - you'll have less payoff, but you're more likely to be one of the winners. Each face can have multiple players' tokens on them (perhaps even an element that rewards co-op [Perhaps it rewards people you have co-operated with the least! Discourage long-term alliances. It's all about public image]) so that the faces all represent different proposals.
Phase 2: The die is rolled. Players take turns playing cards to alter the result - +1 through +3, Surprise Budget for a second result to be added (either player's choice or a second die rolled), Mafia cards to draw more cards, etc. The proposal can also be killed this way. Perhaps it's Condottiere-style play until you pass, or perhaps it's Poker-style. Maybe the number of times around the circle hurts the overall result: Impetus to get stuff done.
Is this a mechanic for all three Stages/Arcs of the game, or one specific one? Hmmm...
Another thing: Why do we use cubes to track things in Euro games, when we could be using dice? Any time you move a cube on a track, you could just be moving a die, which can relay an additional dimension of information (even, say, the number of cubes that the die represents). Hmm.