Well Accessories do not add anything to a bike when selling it by KBB or NADA. You would do better to sell it with stock items on it and sell the aftermarket items by themselves. For example. I just got my son's bike from a dealer for 4k. It KBBs at 4300. It has over 2k in accessories on it. EASY.
Yeah, I usually find accessories you've added to the bike don't 'get money back' when you sell it (nor do I typically 'pay for' them when buying).
It's mostly just you gotta find someone who wants the exact accessories you picked the exact way you picked them, AND wants them bad enough to pay "extra" for them.
Think of it this way. Let's say we have two bikes that are similar in condition, configuration, etc. Call it two lower-mileage 2-3 year old large displacement v-twin cruisers:
A) Bike with $2K worth of accessories, all in good condition, priced in. It's maybe $1,500 - $2,000 more.
B) Bike with no accessories, just stock, priced that much less.
So assuming the underlying bikes are equal in all other regards, I'd need two things to consider A: 1) They were the EXACT accessories I wanted and all in great condition, 2) pro-quality installation, no crappy wiring or funky stuff. I -might- in that case justify paying near-new prices for used accessories as a trade-off between the time/effort to buy my own and install them.
Basically if even one thing on bike A isn't my bag, e.g. a premium seat I don't like, then A doesn't make sense for me any more. I'm paying for a seat I'm gonna pay to replace at that point.
But also bear in mind... A may fulfill ALL my conditions and I go with B anyway for something like... I prefer its color, it's windshield is a better height for me, etc. Or they're not exactly equal and I go with B because it has new tires vs. A's need replaced soon. Or it has 1,000 less on the odometer than A. Or whatever. With B I can always
add my own brand-new accessories just exactly as I want them. I don't -lose- anything by going with B, so something minor can tip the scale because "Well hell, I can always add those same accessories for about what the guy's asking."
Now reverse that and say A and B are close in price. THEN it all changes... Maybe A is $500 more, so I'm basically getting the accessories at 25% of new - more realistic for used items. Suddenly there's a bit of room to say "I don't like that seat, but I am getting ALL that other stuff I do like, and it's all installed, and I'll come out ahead even having to buy my own seat."
That, IMO, is exactly why you 'rarely get much money out of' accessories (vs. their new cost) when you sell the bike.