Building time is always slow, but I think I have a solution! You can send multiple builders to work on a single project, so the time can be reduced. So with two builders, a building's construction/upgrade time will be halved, with three, you will only have to wait 1/3 of the time, etc. The current time should be reduced, not the overall time.
It's been suggested. But if it's added, I'd expect they wouldn't give a full benefit. i.e. 2 builders = 150% build speed.
Yeah. It has been suggested. Check out the master list for each of the request forums before posting. If your idea has been suggested then it will be on that list.