Canon 28 mm: f/1.8 or f/2.8?

[supersleeves]

I currently own the Canon 50 mm f/1.8 and the Tamron 17-50 f/2.8 and am in the market for a new lens. I want to get a prime (I like how light they are and the simplicity of the fixed focal length) and was looking for something on the wide end. After some research, I am torn between two: the Canon 28 mm f/1.8 and the Canon 28 mm f/2.8. First, is it really worth the extra $200 for the extra few stops (I shoot mainly band photography and my friends, substuting flash when light isn't good enough)? I heard the f/1.8 is soft, sharp, has good contrast, and fails in comparison to the f/2.8. Opinons? Also, with the two main lenses that I own, is it really worth it to pick up the prime, or is the Tamron just as good (save for the fact that it is a zoom)?

Opinons?

[supersleeves]

I am also considering the 35 mm f/2.0... is this a reasonable substitution for either of the aformentioned lenses?