Using a strict # as the early win bonus unfairly favors one victory condition over others depending on the map. If the bonus is too high, then spaceship victories cannot compete with an early conquest/domination. If the bonus is too small, then milking will still win.
GOTM12-Kemal had a very early spaceship launch. He won at 1385 A.D., so his bonus would be 8,190 (273 turns*30). I got conquest at 540 A.D., so the bonus would be 11,130 pts (371 *30). Could Kemal have 'milked' 3,000 more points during those 98 turns, while still trying to launch his spaceship as early as possible? Before the game added on it's own early win bonus he didn't have 3000 pts, let alone having that many more points higher than my base score. Did I play a better game than him? It's hard to say, but I don't think so. We had two completely different goals, so you can't compare.
There are many factors that go into how much an early win bonus should be given that any strict number doesn't take into account (map size, land %, # of opponents, land formations i.e. islands vs. pangea, which victory condition you are going for, etc.). The proposed scoring system that Aeson has posted in the other threads look much closer to what the optimal system should be. There are different bonuses based on the map specifics and which victory condition you go for. There may be some situation early on where it may look unfair to some victory conditions, but hopefully we will get those more evened out as we get more results from various playing styles and results of games. No formula will be perfect, but Aeson's looks like the closest we are going to get for awhile.