In "Winning Tactics against Drow" (
http://www.wizards.com/default.asp?x=dnd/tt/20050719a) from WOTC it specifically mentions, "Darkness creates an area of shadowy illumination, impenetrable to darkvision or low-light vision. By itself, it's an interesting option and most useful when the drow are encountered in an area familiar to them, but foreign to their opponents. The final spell-like ability drow have pairs superbly with darkness. Drow are clever enough to place their faerie fire spells to good advantage, outlining the player characters and making them easy targets. (Though DMs should note that darkness will affect faerie fire's ability to work if it's a 2nd-level or higher effect; a drow's spell-like abilities have a caster level equal to the drow's class levels.)"
So it seems to me that you can basically "heighten" any spell-like ability as desired by this interpretation, casting Darkness as a 2nd level effect and Faerie Fire at 3rd.