Is it worth it to mine with what you already have? probably yes, is it worth it to go spend a boat load of cash and build a dedicated mining rig? personally I say no.
I agree, I've been crunching the numbers and have decided against buying a new dedicated mining rig and just modifying my existing gaming rig. It's cost me about $200 and will bump me up from 120M/hash to 700ish.
The fact that I have four months left on a housing lease where I have unlimited electricity helps make things a bit more profitable too
