External Hard Drive Upgrade or Storage Array/NAS

I am currently a college student who has been interested in photography for the past two years or so.

Right now, my storage is as follows:

2 2tb Western Digital MyBooks

1 1TB Western Digital portable external drive

1 500gb Western Digital MyBook for Time Machine Backup

For the 2 2TB Western Digital Mybook I have it partioned for a 1Tb clone of my Western Digital external drive, 300Gb partion of a clone of my Macbook, and a 700GB partion for photos. Currently I have about 680/700GB on the photo portion, 500GB on the 1TB external drive along with 300GB of an iTunes library on that same drive, with a 170GB/300GB of my Macbook clone.

I know that I will surpass 1.5TB of photos in this upcoming year. Does it make sense to purchase just two new 3TB external drives to replace the 2TB's? Should I look into a storage array so I won't have to purchase a new HD twice? Should I buy a NAS? Any thoughts would be appreciated.