i currently shoot a 40D and one of the lenses i have is a 16-35 ultra-wide and honestly, i say save your money and/or get a shorter lens if you REALLY need the wide-angle. the 16-35mm isn’t as effective of a wide-angle due to the 40D’s 1.6 crop. the results from a 16-35 would look more like a 26-57mm (respectively) on a 1.6 crop camera. to compare, from the shots that you have been taking it looks like you are fairing out fine without the 16-35mm ultra-wide. in fact, i would most likely produce the exact same shots that you’ve been taking with my 40D and my 16-35. the wide-angle features on the 16-35 ultra-wide only becomes apparent when shooting with full-frame cameras (eg. 5D Mark II, 1Ds Mark III, etc.)

if you need something wide with a larger aperture, there are a few alternatives for a wide-angle. the $$ not an issue way, the 14mm 2.8L II USM lens is nice/sharp lens with little distortion/fish-eye effect that needs to be correctin post-processing — with the 1.6 crop the 14mm will look more like a 23mm wide angle. the cheaper way would be either getting: 10-22mm f/3.5-4.5, 20mm f/2.8, a 15mm f/2.8 fisheye, Sigma 10-20mm f/3.5, Sigma 15mm f/2.8, or a Tokina 10-17mm f/3.5-4.5 fisheye. the solution for the fish-eye distortion would be to post-process using a distortion correction program like DxO. the non-fisheye lenses would produce better results due to less correction.

just my $.02
sorry if that sounds confusing.