Not a dealer, but I did stay at a holiday inn express once...
my guess is even on resale fo the traded in boat, the dealer doesn't get much for the extra goodies... it does help to move the boat, but a knowledgable buyer will only want to pay close to the book value for the boat/motor as well...
It truly is a pain when trying to trade in, and not feel "bent over"... I personally dont want to have the hassle of selling it myself (look how long it's taken Tox)...
On my last trade in, I got the dealer to throw in a number of freebies (black light installs, sonar installs, etc...) to help offset some of the things, but coming down on actual price was never an option.