WW is right. We, like pretty much all dealers go by NADA when it comes to trade value. What Ducati is doing is based on the bike you are buying, re: looking to trade for an 848 would yield an extra $400 over their TIV(just an example).
Just be cognizant of the whole deal. Some might try to give your trade something less in order to take advantage of the allowance. This would basically give them the allowance from Ducati but give you nothing. If done correctly, you can end up with a nice trade in value for your bike.
Personally, do the free service in stead of the extra trade $. Look at the program, it's one OR the other. If a deal is done correctly, you can walk out with a great value on an 848 and nice TIV for you bike.
One of things people fail to remember is that they want max value for their bike with the lowest price for the new bike, heck we all want that BUT it doesn't always work that way. Would you sell your bike for the lowest deal, then buy one for the highest price? Their is a margin in which a dealer can play with and sometimes it works and sometimes it doesn't, their's give and take on both sides.