Not really. Consider that during the entire game you will only complete 504 marketplaces. By choosing the right strategy you will get 4 more points for each of those completions (as in your example 24 instead of 20). That's a total of 2016 points!
... but wait! ... 2016 over the entire duration of the game. But the final score is the average over 540 turns. That 2016 gets divided by 540 good sir! You add less than four points to your milkrun for that game
...
@rysingsun: Thanks for your response.
In addition to what Lord Emsworth has stated about the level-multiplier, there are some other major implications/considerations:
1. Your example of getting 4 extra points is flawed!! Only if you get the 504 Marketplaces on the last (or penultimate) turn will you get 4 points!
If you get all 504 Marketplaces (unlikely in practice) by the middle of the game (highly likely), you will get at least 1008 extra points!!
2. You have not taken into account other builds that are affected by the internal workings of the game.
For example, say you have a city with 12 Happy People and NO Hospital. Now, if the Food Box is full, you can (cash-)build a worker (very useful) knowing that the city will go back to 12 Happy People at the end of next turn.
However, your strategy may change depending on whether the game calculates the score going
IN to the end-of-turn or coming
OUT of it.
For example, if the game calculates it coming
OUT, you may want to give up 1 of your City-A tiles to neighboring City-B, making City-A's 12th Happy Person a Specialist, so that you lose only 1 "turn-point" instead of 2. If the game calculates the score going
IN to end-of-turn, you don't have to think about what to do until next turn.
Apart from building Workers & Marketplaces, the same strategy question is applicable to building Settlers, Temples, Cathedrals, & Colisseums.