Creepster,
You are on a voyage of discovery that a number of us have already suffered through. It makes you feel sort of cheated to spend all that time on researching the future techs only to find that they have so little net value. I can't figure out if this is a mistake on Firaxis's part or if we just do not know how to trigger the special FTech bonus.
Let's ask your question another way:
You researched 17 future techs at a cost of 4000 gold each.
If you already have a citizen working every square of dirt, coast, and sea in your empire and every person was ecstatic, then you may not have been able to use the gold in any other way. Otherwise, what could you have purchased with that 68,000 pieces of gold that would have produced more happy people or more specialists?? Doing things to enhance these numbers seems to drive up the per turn score at a much higher rate than any future tech impact.
For that matter, you can extend this logic backwards to any technologies that were researched after you obtained total control of the game.
In my GOTM10, I shut down research after getting Cavalry and never researched anything in the upper branch beyond theology even though I continued to play for about 20 more turns.
If I had been milking the game for maximized score I am not sure I probably would have researched to get mass transit and then shut it down, but that would have taken mooooooooooooore patience.