Mixing up components....chain switch?
 

Started with a full 105 set and now will be changing the cassette to the Ultegra 6700 as well as the RD...should I swap the chain for an Ultegra or is it ubercritical?

Drivetrain has 20 miles on it so wear isn't a problem.

Not sure if I really like the new DA chain with the quicklink...heard it needs attention much sooner than the other chains....is this true?

Is the Ultegra chain or even the DA chain a worthy upgrade mainly for smoothness/ weight or just keep the 105?

save the money and keep 105 til it wears out then upgrade if you want.