Trade-In iPhone 4S for iPhone 5S?

I have a 16GB iPhone 4S, perfect condition, been in a good case for 2 years, screen protectors on both sides. No damage at all. I want to upgrade to a 5S, but not sure if I should trade my 4S for it and lose my 4S, or keep my 4S and buy the 5S.

I'd like to have my 4S around as a secondary phone for taking pics and storing stuff on it.

But if I get a 64GB 5S, then that's gonna cost $400, and I spoke to an employee at the Apple store who said I could get up to $190 for my 4S. That would make the 5S purchase a lot cheaper.

I just want others' opinions on this and what I should do.

Should I trade in my 4S? or should I keep it and buy the 5S?

Is it worth trading it in?