Yeah, I think the "shimmering", or whatever it is, is "normal". The engine wasn't build with Anti-Aliasing, so it has to be forced/applied by the driver. This is a rather brute method; usually more costly with less quality as compared to actual in-game AA. The shimmering is probably a side-effect of this, or it may have been there from the start, not really sure.
The side-effects of enabling more than 4xMSAA and gamma correction is the thinning of smoke and the disappearance of the sun's halo respectively (IIRC, correct me if I'm wrong). If you never look at the sun and don't mind a bit flimsy smoke, then by all means, set it up as you want.
* that setting for Anisotropic Filtering is also highly recommended; it makes textures sharper, particularly at distance (has to do with the angle at which you look at a surface: the shallower the angle, the blurier the texture). 8XAF should be manageable for a midrange card and gives good results. Going from 8x to 16x has very little benefit while still costing some performance (on the better cards it's hardly noticeable, if at all though).