Director Tim Burton's obsession with late horror maestro Vincent Price is reaching full bloom. Beginning his career with the 1982 animated short Vincent (about a young boy obsessed with you-know-who), Burton is currently directing an hour-long documentary, A Visit With Vincent. ''Tim saw Vincent's movies when he was growing up and felt a bond (with Price's) haunted, driven antiheroes,'' says Lucy Chase Williams, author of the upcoming The Films of Vincent Price and a consultant to Burton's film, which will possibly be a direct-to-video release. ...After enduring critical wrath for his ''accented'' movie roles (in Bram Stoker's Dracula and Much Ado About Nothing), Keanu Reeves has apparently taken the hint. For his stage appearance as Shakespeare's Hamlet in a Canadian production opening in Winnipeg in January, the Canadian-raised actor has hired a voice coach. Director Lewis Baumander says he gave Reeves the idea after rehearsing the play's ''To be or not to be'' soliloquy. Sometimes action can speak louder than words.