[dumbluck]

Perhaps if the multiplier is randomized. For example, your low/medium/high tech cost games have multipliers of 1, 2, and 4 to your "base" tech costs. Instead, make them a random number within a range. An example would be 0.80-1.20, 1.60-2.40, and 3.40-4.60. Then if I chose a low tech game, the computer picks a random number (1.12) and all your base costs are multiplied by 1.12 THIS time. The next time you play a low tech cost game, the random multiplier might be 0.94, and research would progress a little more than one sixth faster than it did the first game.

Lets look at another example: a high tech cost game. The first game could have a random multiplier of 3.53, and the second could be 4.51. In that example, tech gains in the second game would come about 1/3 slower than in the first game.

I would suggest making those randomization ranges moddable, as well.