Avande - I rode cruisers for 20+ years and never would have thought to ever again get on a sports bike and/or an ADV bike.
Now, I have a 2018 Versys 650 and picked up an old 2007 Ninja 500. Love them both but the Versys...it's a tough one to ever get rid of.
With that being said, I think the current market in used motorcycles is plentiful, meaning that used motorcycles aren't going to get what they're probably worth. The US economy is doing well and most people and dealers are giving better prices for brand new bikes while giving you minimal on trade-in's. Selling outright, it's a toss of the coin. I am always on Craigslist and Cycle Trader just looking. And some of the prices these used owners are listing them for, well...I'd never give them that much!
I think it all depends on how patient you are to sell. I've seen bikes on CL that have been listed for months (at a price I know they'll never get!) but they keep listing and never budging. Meanwhile, the bike is getting another year older and they're losing out.
I'd see what you can negotiate with the dealer first. If they don't give you a decent trade-in maybe ask them for accessories on a new bike. (Helmets, jackets, tank bags, etc...) Sometimes they can write those things off on a trade-in. If they don't want to bargain with you post your Vulcan up on CL and Cycle Trader and see what happens. Ya never know!