I just noticed in DP4 a new option for increasing contrast under Accessibility in Sys Prefs (I only had DP3 before and haven't seen this before). This setting makes the UI elements to stand out better, especially on my 1680x1050 screen. Here you have some pics: https://www.dropbox.com/sh/gwrmyye9z38esl4/AAC7qqDw5y9S-C6wZvBvH-CMa
That seems like a pretty good feature - those screenshots definitely show clearer text.
Which is great - I was a little worried about clarity on my Thunderbolt display.