Well, unlike most everyone else, I've always found NADA to be relatively close, when adding all the option values... and I mean ALL of them. Never consider anything as 'stardard equipment', If it's in the boat, add it as an option. Do that, and the values always seem to fall around asking values I've seen advertised.
I've found this is true with RV's also...
Another factor with NADA- if your buyer needs to borrow money to buy your boat, their bank will almost certainly use NADA values to determine the max money they'll loan. If you're asking $25k and NADA says it's worth $21k, your buyer will have to out-of-pocket the $4k difference..