I wasn't kidding. For a decent sized empire the benefits of mining inc can so soundly trounce any alternative it isn't funny. If you don't have an ubertastic wonder you need, or a corporation already, mid-to-late GEs are for golden ages and corporations.
With fairly small effort mining inc can easily get to +10

(BASE hammers) per city. If you're willing to trade a bit, maybe even 20

. That's not just one city, it's as many as you wish. Yes, there are some setup costs, but mining inc has the fastest payback of all the corporations by far.
If the game isn't going to end very soon, having a 10

mining inc in 10 cities will get you 1000 hammers in 10 turns, 2000 in 20, etc. This very quickly overtakes a bulb, a golden age, and the wonder rush. While the corporation costs money/city, you also get +4 gold per branch in the HQ city. Put wall street there and your GPT won't be going down unless you have some SERIOUS hammers, which is a good thing.
Now, there are setup costs, yes. In reality mininc inc won't pay back in 20 turns, but give it 50 and nothing touches it. Do not rule it out; it's often your very best option. Not always, mind you, especially when you are heavily SP reliant...but frequently enough.