Should I Upgrade to a Retina MacBook Pro or Buy a Thunderbolt Display?

I currently have a 2011 MacBook Pro 13-inch. It's my main notebook, although I use a Mac Pro at work sometimes. I'm considering upgrading my set up a bit, so I thought I would hit you guys up for advice. Here are the two options I'm considering:

  • Sell my MacBook Pro 13-inch and buy a Retinta 15-inch.
  • Keep the 13-inch MacBook Pro and buy a Thunderbolt display, using it as a docking station.

Has anyone done either of these things? If so, how has it worked out?

EDIT: Thanks for the information. I found a refurbished MacBook Pro Retina on Apple's site for about $1600. I think I'll be getting one of those in a few weeks.