I think bonuses should be permanent but each alliance must get some bonus, regardless of how small the bonus will be. If only the best alliances get something only those will get better and better each time and will become unbeatable.
Also I think it will be better to have a winning alliance in each land and an alliance winner for all lands.
And maybe add some bonus land points and let's say when you get 500 points all players that are from that land will get a bonus, 1 point in regeneration or something like that.
I think it is better to have it once every 3 days and maybe at different time intervals, more players will be able to join in, I say this having in mind that we have players from US and Asia also, not just from Europe and we're on different time frames.
I'll get back with more later on.
Cheers