I currently work in the Automotive industry as an asset manager. I put over 2,000 vehicles into the used car market last year and have some advice after reading through this thread.
West coast only uses KBB. Typically everyone in Texas will use NADA Book value or MMR Auction value to give you the value of your trade.
Dealers are hardly making any money on new vehicles now a days. They won't make much if any on the front end (the purchase price) but will on the back end (financing, warranties, any thing offered to you by the finance person). I don't think I would ever buy a new car because it is a deprecating asset and especially in that first 1-2 years. I have leased the past two vehicles for my wife. I always advise this is you can adhere to the mileage restrictions (these are negotiable too.)
There is some really good advice about negotiating on this thread. Pinning dealers against each other, doing it by email or text, knowing what you want your monthly payment to be.