Go ahead and low-ball them. Since you have a Diavel, they know that you're a serious buyer. My friend came up with a stupid deal to trade his '11 S1KRR in for a '13, and he called all the dealerships within 100 miles and flatly told them "the first one who says yes gets my business." The 2nd dealer he called bit on his offer.
Not sure where you live, but if your winter is harsh, most dealers know that this is the last chance to sell bikes before hibernating for the winter or hoping a Florida, California or Arizona buyer is willing to pay the shipping. They don't want to pay floorplan for 3-4 months, so they may do the math and take a low-ball offer. '14 bikes will show up in March so they'll get more motivated the later it gets. Lastly, Ducati will come up with a spring promotion to blow out the pre-14's. I bought my leftover '12 Pani in April this year when they offered 1.9% plus first 6 months payments. Ended up buying the $17,999 MSRP bike for $16,300 OTD, less another $1400 with the 6 payments.
Good luck and let us know how it goes!