If you do a search and notice that the file it chose as your Top Hit in the Spotlight menu is actually the file you were looking for (hey, it could happen), just press-and-hold the Command key to jump right to the Top Hit, then press Return to open that document (or song, email, etc.), which closes the Spotlight menu. See, it even tidies up after you. So basically, just press Command-Return to instantly open the Top Hit. Easy enough.