Edited as I the details were incomplete.
I decided to try the negotiation game for level 1 on my two TE worlds:
I completed 12 check points with the following results for 1st world: 59 goods spent, 5 failed attempts (all attempts were with the 3 tries) and received rewards consisting of coins/supplies, a blueprint, 5 goods, 10 goods previous age, 1 microwave blaster, 1 stealth tank, 1 ultra AP and 10 diamonds.
I completed 12 check points with the following results for the 2nd world: 73 goods spent, 6 failed attempts (all attempts were with the 3 tries) and received rewards consisting of coins/supplies, AM sniper, 1 ultra AP, 1 microwave blaster, 5 goods, 20 goods of the previous age and 10 goods of the current age.
So any negotiation with 3 choices was a guaranteed win, 4 mostly with 5 choices being much more difficult to complete. On no check point on either world did I spend more than 4 tries (I won on the 4th try on both worlds when I did try that many times).
Given the results at these levels I do think there are some general tricks that you can utilize to moderate the goods costs (such as trying over again if you don't get enough information on the 1st turn) but do have to agree that based on these results a 4th try would probably be appropriate for the last level or a decrease in the goods costs. If I remember correctly it costs 3 goods for level III so perhaps reducing that would make the cost more worth while for non-fighters to try the GE Game.
That being said I don't see it being all that appealing to players (I'd fight mostly but might try my hand/luck now and then for a change of pace) but there's no 'hook' for players to come negotiate thru the game.