I am intimately familiar with the latter scenario:
I've just had a great writing week. There are few feelings more joyous than reading back over the week's work and thinking 'that's not bad at all'', as opposed to the all-too-frequent, 'it's rubbish, I've wasted a week and I'll have to re-write the lot.' And if you think that's an exaggeration or false modesty, you are very, very wrong. It's perfectly possible to put in eight hour days and have nothing to show for them but a single idea that, if reworked completely, might be passable.
Jo Rowling,
quoted at The Leaky Cauldron.
Actually, taking a couple of weeks off is helping me immensely. I need this distance from the amount of writing I've done since the beginning of August.