My Bernina dealer has prices with trade in and without, they are listed on a card, and they don't negotiate- no cash discounts, no added accessories, they stand firm. I'm pretty sure the "with trade in" is a way to offer a price below MSRP. I traded in a Kenmore that cost $200 5-years previous and got a $600 discount on my purchase for it.
If I were to buy another machine from them, it would make more sense to buy a new machine at Walmart rather than trade in my current machine... (I don't know if they would offer a better price on a machine they could resell- they send their trade ins to a charity)
Another dealer (Janome) I went to appraised the trade in and only took machines she could sell. Mass market or low end machines were not taken.
So you need to figure out how the dealer handles trade ins to decide whether it would benefit you or not.