Graybeard
You are grasping at straws.
Will the KC30/45 haul the dense, outsized cargo the C-17 carries?
I assume that was a rhetorical question, because if you meant it then the answer is obviously "No, obviously not!". They can be used for pax and freight just in the same way as the KC135 and KC10 can be, and are. Only you can get a lot more pax and freight into a KC30 AND still do the tanking. It makes deployments a lot easier.
Buying planes with a third of their hours/cycles left is prudent economics. Look at all the 747 cargo haulers carrying the USAF loads today. They are upgrading to 747-4 to save fuel, not for longer life, or because they are new and shiny.
Only if you plan to use them and burn them out and then replace them with the next generation of airline cast-offs. I can't see the US taxpayer being happy with having to replace inefficient, out-of-date, expensively modified tankers in 15-20 years time when they could buy a brand new fleet that will last 30 - 40 years.
The fact is that second hand aircraft will become more difficult to maintain, are less efficient, will require expensive upgrades to maintain compliance with items such as GATM and will have a shorter operational life than new ones.
Trying to justify spending $40 Billion based on ancillary uses shows the weakness of the primary argument
Not trying to justify the purchase based on ancilliary uses, it just demonstrates that you get an additional free capability whether you choose to use it or not. Lets face it, if you don't need all your tankers on any one day then you can use them for freight and pax. Therefore you don't have to charter from Evergreen etc and you save the taxpayer some $$$, or you free up $$$ to spend on other equipment programmes
The fact remains, as demonstrated in keesje's post below which I wont bother copying again, the KC30/45 is a far more capable aircraft than the hybrid 767 and its cheaper!! If the USAF choose to employ them as flexibly as possible you save money. Buying second hand doesn't make sense in the military.