Upload & Sell: On
1. I shoot mostly landscapes, but when I use these two for things like stars, nighttime, 2.8 looks pretty good on both - although my experience is VERY limited. I CAN tell you both lenses are crazy sharp at landscape apertures, WAY better than my 24-70 (and I have a very good copy of that lens)
2. Honestly, I'm not really put off at all by the build quality of the 28. It's not in the same league as the 24, but it's still good. (And I'm sometimes pretty tough on gear). The flip side, as was mentioned above, is the 28 is small and lightweight.
3. Personally, if I had to pick one I'd go for the 24. I like having a little wider view and the 1.4 comes in handy at times (not that 1.8 isn't still pretty great).