You could simplify that by getting a complete media center, like WD TV Live Hub(which is top notch) or something similar.
It's more expensive than a simple wifi hard drive, but well worth the price imo..
+1 on this. I love my WD TV Live Hub. I wish it had more HD space built-in as 1 TB get filled up pretty quickly with 1080p movies, but plugging external USB drives into it works very well and I can access all the movies with my N4 or Xoom.
I guess it comes down to what you are looking for. I would think about getting the Wi-Drive since it is portable giving you the ability to watch movies on your N4 anywhere and for extra portable file storage. The WD TV Live Hub gives you a lot more space for your buck, ~$200 for 1 TB on the Hub versus ~$100 for 64GB on the Wi-Drive.
This thread has me thinking about creating a folder on my Live Hub just for expanded storage for my N4. I already use my N4 to control the Live Hub, so why not use the Hub to make backups of my nandroids and rom files.