I also would really like this feature of spotlight and use it often. In addition to what @kaumac mentioned, the nicer aspect of Spotlight is that you don't need to type the destination currency for most common ones. For example you just enter 100USD, and you get the equivalent of that amount in Euros, British Pound Sterlings, Canadian Dollars, Swiss Francs, Japanese Yens, etc.. Or you just type in 50GBP and you get the same. Really love and use this feature. Had to keep the spotlight's hotkey for now, although I would like to use cmd+space for Alfred because I'm very used to that hotkey.