When I use spotlight (on Yosemite 10.10.2), Quick Look doesn't display a preview in the right panel anymore. Only when I click on a folder in the left panel it displays the contents of the map in the right panel. But when I click on either a .pdf or a .pages file in the left panel, the right panel is empty, whereas a few weeks ago it still did display a preview in the right panel in those cases.
Do you have "Show Preview" or "Hide Preview" in the View menu when Finder is in the foreground? You can turn the Preview off and on with SHIFT + CMD + P.
However, the preview pane only works in column mode.