Gerdler touched on the point that I planned to make. The only purpose of the NPC countries is to make the game more fun and enjoyable for the players. The principles that guide their actions do not and should not match what an individual human player might do in trying to maximize NW. Farmer is the best example. An "optimal" farmer might save the first 720 turns, then sell food on private every turn in order to get as much tech as possible. What would happen if all of the NPC farmers behaved as such?

1) There would be little to no food available on the public market for at least 60% of the round. Every player would need to build farms.
2) Techers wouldn't be able to sell their agri tech, so logically they would stop producing it. Will the farmers actually by able to find agri tech once they start playing turns?
3) Indies wouldn't be able to sell their military units.

Does any of that sound fun to you?

NPC countries have a large percentage of the server's overall buying power. The change that you are proposing ("NPC countries should wait for cheaper tech") is not at all simple to implement. If market history suggests that the best time to buy tech is 48 hours into the round and enough countries try to buy tech then, suddenly that will no longer be the best time to buy tech. Frankly, I don't even see the issue with some NPC countries sometimes buying tech over $4000. Why is this a problem?

For the record, I think that 16 M NW is a pretty good finish for a country that got landgrabbed 36 times for 8k acres.