Yeah, my argument for the Thrux would be......do you want to be like a sheep in a herd of thousands (the nightster) or do you want to stand out and be a little different than the herd, like the sheep dog. Be the herder not the herd, get a Thrux.
Nightster: 553lbs dry, 72bhp with aftermarket intake and exhaust, $10k + whatever the screaming eagle add ons cost
Thruxton: 452lbs dry, 68bhp without modifying the intake/exhaust, $8800 msrp
huge performance advantage to the thruxton, with $2-3000 left in your pocket.
That's not telling the whole story. That 1200 motor is a torquey sumbitch. It's power delivery is totally different than the Bonnie/Thrux.
I think all you need to do is have him test ride both & decide, they are totally different styles of bike.