Yep, CS4 is the latest version. Outrageously expensive, unfortunately, but I've owned PhotoShop for years and tend to upgrade only on alternate releases which helps. I'm sure there's other software out there that could do a similar job. Yes, I've posted a few images on the forum.
I did a quick bit of post-processing to illustrate the effect of a graduated filter. The filter was applied from about halfway up the picture and ran up to the top. It was used to apply changes in brightness and contrast, with the strongest effects at the top. I then added some tweaks to the whole picture increasing contrast and vibrance. With your permission, granted via our exchange of PMs, here it is:
I've probably overdone the tweaking a little but I wanted to show the effect. It's also debatable whether I should have masked the tall building on the left from the full effect but I chose not. All processing was done using Adobe Camera Raw, which is part of PhotoShop. By the way, I'm just a "happy snapper" so please don't confuse my own take on what might be done with that of anyone authoritative. There are many members of our community who are much more accomplished and artistically inclined than I.