[Beck]

I'm guessing that is an in-house deal since the standard street price for a $20 donation is $3 million. It's tough get actual value on the street because of the aid slots. For a really large nation, $5 million for your donation is cheap. I know nations that $5 million will only buy 50 points of infrastructure when you get 200 for the donation.
I overpay for tech if it's with an alliance member since it serves as aid and I get what I want out of the deal to boot. I'm in the process of buying 135 levels of tech for $3 million, normal street is 150 levels for $3 million.

Definitely only swap out when you have the money to replace it. +1 happiness is better than nothing, it's $2.00 on citizen income unmodified.