[Klaus]

Welcome back
Unfortunately, I have some bad news for you....Not having enough motivation to swap lenses and staying on a single lens all the time, is a sign you're advancing in age....
if you're complaining of the constraints for travel because of  GF, wait till you have a daughter

It wasn't about motivation, really, but I never really felt the need to go beyond 70mm.
Maybe it would have been different if I didn't have the 70-200mm f/4 but a 90mm f/2.8 or so. Having not taken the Sigma 90mm f/2.8 was probably not the right thing to do.  However, it taught me - again - that a 70-200mm f/4 is somewhere in no-man's land. 

And yes, getting older may also be part of the problem ;-)

Having said that - I'm fairly pleased by what the 20-70mm f/4 gave me.