Yes... it is right. It's a platform that flies a very docile 1G profile. And not overly complex, like the C-17. In fact, not very complex at all. There is very little wearing out on them. So, yes, 50 more years is reasonable, even though you scoff at it. If you know something I don't, then let me know.

That may be correct. But you know what? The GH has already been through 2 Nunn-McCurdy breaches. How much more are the US taxpayers going to give to Northrop Grumman before they will consider this turd polished?

Imint versus Sigint? How about both! There is a huge synergy when those work together. The GH has very little SIGINT capability. Yes, they are "working on getting it more"... but as was mentioned, they GH is out of electrical power.
Enduring: remember the NASA Helios UAV test platform? It flew for a long time, and reached almost 100,000'. So would it be a good ISR platform? No, obviously not. And "experts" need to quit getting wrapped up in the whole "it can stay on station for 24 hours". So could the Helios. Or a hot air balloon. Big deal. What "equipment" is going up with it that will let it actually do the ISR mission?

Also remember: if you want to transit across foreign countries, it is much easier in a manned aircraft. Why? Because many nations will not even consider letting a foreign military's unmanned aircraft go through their airspace.

Yes, I'm still associated with the U-2, and am biased.
But I'm also a taxpayer that wants what's best for the country.
There will come a day when the U-2 will not be the best ISR bang for the buck.
But that hasn't happened. The GH cannot do the job near as well as the U-2.