It´s NOT a personal Oracle issue here, but a general one. The ENABLE procedure turn the BUFFER on, but sql*plus can´t "see" it´s on by itself, the setting needed to do it is the SET serveroutput on.
Note : ANY setting in sql*plus environment (linesize, screen echo, page size in screen, etc) MUST be done using a sql*plus command called SET (or using the menu, in GUI mode), and PL/SQL don´t understand sql*plus commands (SET or whatever - PL/SQL just "knows" PL and SQL commands). SO, the environment must be ready BEFORE the PL/SQL runs : you can do it in a PL/SQL script BEFORE the PL/SQL block, OR automagically habilit put the sql*plus commands in the login/glogin script.

Regards,

Chiappa