So i am assuming a taller building doesnt translate into higher density?
The "tallest" buildings are high density *and* high wealth. High density but medium or low wealth buildings are still high density, but aren't visibly as tall. That said, density goes down as you go up in wealth. For example, a high density low wealth residential building holds 600 sims, while a high wealth one only holds 100 sims, even though they both cover the same amount of land. Therefore, your density level didn't change, but your sims went down because your wealth level went up.
Also does the value of exporting TVs or Computers ever go down?
It is supposed to be dynamic based on supply and demand, but Maxis/EA hasn't enabled that aspect of their simulation yet.
And is it possible to have the Willis Tower + Empire State building in the same city and they both make money? Two of my cities have these and neither can make them both profitable. It is either one or the other.
You probably don't have enough tourists or ways to get them into the city.
Also if I build the solar array in the great works will it provide enough power for the surrounding cities?
I think it provides something like 18,000 MW which should be more than enough to run every city in the region.