Need to Upgrade Time Capsule

I have a 2nd Generation (early 2009) 500GB Time Capsule, but I'm quickly running out of space. I want to upgrade my backup solution to 2TB so I have plenty of room to grow. My question is, what would be better: Purchase the new $299 2GB Time Capsule, or purchase a 2TB external hard drive and plug it into my existing TC via USB? Thoughts? Anyone else upgraded an existing TC with extra storage via a USB-connected external hard drive?