I don't have the 12-35, but I'm sure it's a very good zoom lens, and it's near the top of my list of potential future lenses, though quite a ways off. For me, it would replace the 14-42 v.II that I own. I don't have the 14-140 and doubt I will get one of those.
It seems to me that the 12-35 considerably overlaps with the lenses you do already have. You have the 20 and 25 when you need fast and sharp, and the 14-140 when you want zoom convenience (missing only 12 and 13mm).
Since you want a wider lens for landscape and city architecture, either the 7-14 or the 9-18 would make more sense to me. An ultrawide really opens up a lot of possibilities that you just don't have now, and both cover the 12-13 range you'd gain with the 12-35.
I have the 7-14 and like it a lot with my GX7. I chose that one over the 9-18 because it's a bit wider, reputedly a bit sharper, and constant f/4. However, the 9-18 might make a more sensible walk-about lens in a city with its 18mm long end, and it's cheaper, lighter, and takes filters on the front.
I'm sure the 12mm f/2 lens is very nice, but it's always seemed overly expensive to me, given that many give it somewhat lukewarm marks for IQ. If I'm going to pay that much for a prime, I want it to have the quality of the 75. Given the modest difference between f/2 and f/2.8, I'd take the 12-35 over the 12.
