I can totally understand the question. Why pay full price for a game that has been out for so long. And on most games I would agree.
But then again, on most games you would need an incentive to jump in so late. On monst games, going to the forum even one month after buying it will totally ruin it for me. On most games there would already be lists of walkthrus, and exploits, and easter eggs, and always-win tactics.
This game has been out for years. And we all KNOW that there are some nations that are too powerful, and some that are too weak, and some exploits no one should use, and some killer strategies. But the real glory of this game is that even after years of discussion we still cannot agree on what those are.
We are still debating them. And trying various mods on them. And daily enjoying the testing of new strategies and tactics. There are not many games that fall in that category and I would have no problem paying full price for them for as long as they can maintain that new-game exploration factor.
Just my opinion
Gandalf Parker