The web has gone through fits and starts- your job may seem stable now but how much warning will you get when demand shrinks for web development and your employer can't afford to keep you on?
Furthermore, getting that graduate degree in a real discipline is the surest way to tenure at whatever career you pick. That tenure translates to hundreds of thousands of dollars over your career.
Furthermore, getting that graduate degree in a real discipline is the surest way to tenure at whatever career you pick. That tenure translates to hundreds of thousands of dollars over your career.