Is there any real benefit for building more then the "+3"s??

I just read the wiki page that Dan posted on here(thanks again for all the hard work Dan!)
and I noticed that the cost of the +6 to mining for example(I don't remember name of building)
costs 10M credits for 15 space.

Now if you do the math...take 30 space to build...the +3 take 9 and the +6 takes 15....

So that's-

3 of the +3 to mining = 27 space = +9 to the mining
2 of the +6 to mining = 30 space =+12 to mining

Now considering that the +6 to mining costs some 9,950,000 MORE TO BUILD are these buildings actually worth getting? The benifits dont seem to go with the price of credits and space.

In the long run it's always more interesting ... And even more if your planets have high ressources ratio, the kind of planet you want to save space on for some defence or cloak for instance

People suggest and I can see why, only upgrading your planets every 2 research tier upgrades.

my strategy is, +3 (cheap darrynite) building on my buildings>rich. then all rich ones i keep a mix between my highest 2 buildings(depending on special buildings/defense) i.e. a planet with 9x mega rich artifact is definitely going to pay off the extra money you put into awesome planetary buildings, while a Abundant one will not.

you have to remember that the amount you have into mining research artifact on a planet are multiplied by the resource bonus and the development bonus. So just +1 artifact on a x6 mega rich planet offers +9 artifact points per hour(350% resource bonus and 200% development bonus), and assuming you have control over this planet for a month. Thats 6480 artifact points. off of just one extra artifact structure on a nice planet. So in the long run, every point counts, and thats why were playing this right?

also i like the idea of upgrading structures every 2 upgrades, but i might be too impatient for that

Use the best structures you can afford. If you find that you can't build your best structures then you've probably out-teched your income. Once that happens focus your efforts on researching other tech trees and try to increase your mineral intake. As you gain ranks each point of minerals will tend to yield better and better ore, I think that yield peaks at rank 100, but Dan mentioned he was thinking about raising it.

In my opinion, 4 is a good place to stop. 5 & 6 don't do much better for the space, although 7 & 8 (yielding 8 and 10 per structure) are awesome. I just finished 7 research and the boost I got was great. But until you are ready to go that far, stop at 4.