If you want new, then new it is. Dealer needs to tell you the price, when he tells you, cringe immediately, and say what's your rock bottom price?
That will drop it another $5K or more.
If you can consider previoulsy owned, a 2 yr old boat is new to me, I bet many for sale on boatraderonline with little 60 hr usage. If motors had 3 or hopefully extended 6 yr warranty, you have some motor coverage. That's the only risk I see, is in the motors, presuming boat is not a salvage or commercial used job.
Then you compare the dealers rock bottom price to the used price.
I don't know how MegaB is doing depreciation, since economic times effects resale not just new price. Supply and demand indicates today the buyer rules. Different if 20 guys are looking for one avaliable model for sale, it's the other way around today.
I use a different gauge, when does the boat reach 50% of it's new price out the door, in how many years? 3 , 5, 7 , etc.
It wasn't long ago the guys with new Marlines figured they could sell in two yrs for what they paid for them. True reality in those boat shortage / high demand times - just a few years ago.
You have your 20 footer just a year or two, you will get pummeled equally on the sale, although the 20 footer has always been in heavy demand even more so lately with people cutting back. Cutting back means down sizing.
I don't know if the dealer will work a deal on the trade in, if so, one advantage to the dealer new option. If you have room to keep the 20 footer around, it will sell and sell better than I bet the trade in can do.
So the only downside for you is the used motor risk and unload value on the 20 footer!