I help designers improve their games.
When I first played this game, I couldn't stand it. Often at least one player would go the entire game without winning a die roll, which is just not fun. It's really hard to win your first card, but then there is a runaway leader problem.
However, I found that some relatively minor tweaks completely changed it for me. Adding a 7th die made getting your first card easier and the bonus for getting that card less of a huge advantage. Tweaking a few other rules further added strategic variation, but the 7th die was the most important change, and I now really enjoy the game.
Here are all the rule changes I recommend:
(a) Seven Dice
Use 7 dice each turn, rather than just 6. This is absolutely essential if you want anyone to ever get anywhere in the game. The cards are actually quite hard to capture with only 6 dice, and your ability to capture cards only improves if you can first capture a few of them -- a real catch 22! With 7 dice, things are dramatically easier, and the game moves forwards at a nice pace.
(b) No King's Revenge
There is no "king's revenge" penalty for failing an attempt to win via the king. The special card that normally lets you avoid the king's revenge instead gives you a 4th roll when trying to win via the king method. The king is still a tough route to go by, and now happens about as often as the other 2 win conditions. Without the change, it is foolish to attempt the king's victory except as a futile act of desperation.
(c) No Starting Castles
Players do not start with castles in play, although a player's last castle is still protected from attack. This is important if you are using the 7-dice change (suggested above), as otherwise the game is over too fast (even for a light filler game). However, you still need to protect a player's last castle, to avoid lock-outs (which just aren't any fun).
(c) Consolation for failure vs. Reward for success
There is no "go again" bonus for successfully attacking a card from the deck. Instead, when you attack a special on the deck and fail, you may immediately try to attack the top card of the other deck. This only works once per turn; if you fail against the other deck, you do not get another attack, even if it was a special. This change makes the game less frustrating when you get a bad roll, and less boring when another player gets a sequence of good rolls.
(d) Using the Blanks...
Use the 6 provided blank cards to make the following custom cards:
They help to further balance the game and make it less frustrating, but they are not essential.
These are some really good ideas, with sound reasoning behind them. I'll have to try your house rules next time I play. Nobody *ever* goes for the King when we play, BTW. We might if there's no revenge.
I agree with your "(c) Consolation for failure vs. Reward for success" idea : it reduces frustration of a failed roll and eliminates 'rich get richer' of a winning roll.
I don't agree with the other ideas, however.