I definitely agree with what codex is saying. Once you know what car you want, you are good to go. I recently bought a new car for my wife and did pretty much all the negotiations via email. Dealers that wouldn't budge got disregarded. Edmunds is a good resource for true market value and incentives.
In terms of cash being irrelevant, I got $3k off the negotiated price as a cash incentive so that may be applicable. They were offering that or 0% (for 3k more on the principle plus tax on that 3k).