Your suggestions about formal war bonuses are good and add to the game. However, the one problem with your suggestions are that you are putting the bonuses too much in the hands of the alliance as it were. You can decide who to war and who to get the bonus off, which may strengthen blocks and smaller-ally farming.
For my suggestion, the aim is to take the bonus out of the hands of the alliance. So saying, youll ONLY get your bonus if u hit THIS ally that is of similar size and count to you (with a good rationale of tension, like US vs USSR superpowers). This will shake up blocks and politics a lot more than if you simply swap from fighting A to B, in which case youd still get your bonus.
There's carrots and there are sticks. If you put control of the carrot in the hands of the people you're trying to tempt, it isn't really effective anymore
