From the standpoint of someone who has been around a while, I think you are mostly missing the point of this game. Without a doubt (or even a close second), the most important thing in this game is space.
I will get all philosophical on you now. Think of this game as a finite universe with an infinite amount of time. FP's represent time. Expansions represent space. In the beginning, it seems that time marches on slowly. One FP each hour as you trudge forward. But time can be sped up. You can buy, win, or wheel and deal for more FP's. In a sense, you are speeding up time. You can advance through the ages without being limited by the tick, tick, tick of an hourly FP. Time is malleable here.
Space is limited. You need to gain expansions in order to increase your space...and expansions are limited.
Other than buying expansions with diamonds there are four ways to gain space.
1. You can get lots of medals and purchase expansions with them.
2. You can advance through the tech tree and gain expansions with each age.
3. You can advance though the continent map and be rewarded with expansions as you do.
4. You can get better, more efficient buildings to place in your city to gain space within its confines.
All of the above require tech advancement. Let's not be mistaken.
As said earlier by nomad richie, balance is required. Some great buildings (Cape, CdM, Inno, etc.) produce FP's so you do get a return on your investment. The Arc uniquely powers up you rewards when you contribute to others' GB's...thus gaining you FP's. The attack GB's (Zeus, Aachen, CdM) allow you to fight PvP, GvG, and the continents which can get you medals and expansions. Traz gets you free troops so you can fight without worrying about losses. It is the most important building in this game.
Again, without mistake, your best bet is to advance technically. You cannot, however, ignore your Great Buildings.
Speaking from someone who awaits each new age, I save some FP packages just to advance through the tech quickly. I usually can make it through any new age now in less than a day. After I do, I can go back to working on my GB's.