Dahon has some bikes quite close to the Tern P20.

I like your idea of having two bikes with your tiny folder (brompton) and a more cruiser/lighter faster bike. I would go with a bike like the P20. I really like derailleured bikes over internal hubs because of the range possibilities and weight and the internal resistance of an internal hub. (many disagree but that is good).

I think Bruce Metris still has a super light Dahon 20th anniversary (in the for sale section above)---under 18 pounds and still like new---$1000.

There have been some great deals on Ebay lately. Look at the chainring and the rims to see how much wear there has been. Sometimes they have practically no miles on them.

There are a ton of options out there. I'm like Bruce in that I would personally stick with 406 20" rims if at all possible.