Yeah, CIZ is good to 1.5x, I never go past it as IQ does noticeably degrade. I didn't take that into consideration, sometimes I forget its there LOL! I have that and s35 mode it on custom function buttons for quick punch ins. But you lose tracking and the ability to place your focus point with CIZ - so all you get is wide AF. But it can be handy since it doesn't impact IQ in any significant manner and it doesn't cut resolution like s35 mode with stills.
To answer your questions, I'm wider than 35mm a lot. I had the Tamron 28-75 and sold it for another 24-70 because I frequently needed it to be a tad wider. I change lenses less now. When I'm shooting I usually have the the UWA or a 24-70 on one and the 70-180/200 on the other body and then switch things up if needed. I even have a 24 and 35 primes because I like that range a lot. I really wish Sony would do a better 28 so I could consolidate both, its a happy medium for me.
But utilizing the CIZ with 150mm on the long end effectively negates the shorter range in many situations. I have glass beyond 200mm too, but that's a specialty lens that's not in my daily carry. I'm pretty sure a high IQ UWA zoom and the 35-150 would work well for the way I shoot, and for a small chunk of that range I'd get a bit more light gathering than the 24-70. I *think* I'd be more efficient being able to use the zoom and crop options to extend the reach.
We'll see. I'm in no hurry to sell off a bunch of gear and buy two new zooms, despite the fact new stuff is fun. I'll probably rent the Tamron for a long weekend and tinker or wait for used copies to start popping up on Fred Miranda and get one at a bit of a discount.
I've also been looking at the Freewell magnetic VND's and such to further simplify my kit while staying versatile. Right now I have screw on filters and a 100mm filter holder with a bunch of filters I don't use very much because of the time it takes to setup. I always just wind up using my VND's, even for landscape photos and such - which I shouldn't do since I have the big/little stoppers, a CPL and a few ND grads with that NISI system. But its hard to be more run and gun fumbling with large glass plates.
Cheers
Chris