The standard reply on this forum when someone asks "what's my bike worth?" is $3.50, but I like that bike, my neighbour had one when I was a little kid and I thought it was about the nicest bike I'd ever seen.
Sadly he was killed in a car accident and his family sold his bike, but I still have memories of riding on that back of that thing and thinking that life doesn't get much better than that. I've owned a 350F and it was a great bike too, but no faster than the twin, so if you can afford it, keep it, in my opinion the later 350/360/400 twins weren't as nice. Cheers, Terry.