If you can afford it, I would do it!!!
You can look to add either the Intel X25-M G2 80GB or OCZ Vertex/Agility 2 50GB SSD's for under $250. If you can stretch it to closer to $400, I would get the 100GB version of either Agility 2 or Vertex 2.
Also, you can look to go with the OCZ Vertex 2 or Agility 2 50GB SSD drive and up your GPU to an ATI 5770. This would make the system a decent gamer build even at 1920x1080 + resolution.