I think it should stay the way it is. Promotion to League 2 means as a club, you have earned yourself professional football club status, this is by far the biggest honour for the vast majority of clubs in England to obtain. By having just two promotion places in the Blue Square Premier, it keeps it exclusive and that bit more special when clubs do win professional status.
At the same time, by having just two relegation places in League 2, it helps clubs retain that professional status and protects more clubs from falling into a potential financial abyss that would come about as a result of loosing their place in the football league.