Planning cuts down work in the long run, it saves having to go back and rewrite stuff relentlessly, because you find yourself with major plot dilemmas. To me, a good plan does not take the fun out of writing, it puts less pressure on you to make the story flow. The fun part is taking the information and turning it into something pleasurable to read, rich with well written prose, flowing dialogue, and interesting narratives.
It is hard enough to make the story readable without having to worry that you face 6 months worth of rewrites because the story went somewhere you didn't want it too, or a plot line just doesn't make sense, or you have too many loose ends to tie up.
Of course, that's not to say its easy to plan every detail out before you write it. So, you might end up writing a basic plan of how your plot will develop, and then discover everything else as you're writing. But yes, I think most, if not all, successful novels are planned to the hilt before the author even puts pen to paper. But that's a skill that obviously takes time to develop.