We left everything in ours for our last trade in. The new one had everything we needed and wanted, plus more. If I would have kept all the add on stuff I put in, I would have just had put store more stuff somewhere at home. So we just let it go with the camper.
I even threw in the original awning, even though it was shreaded on one side. I tossed in the second television and mount on the wall. We don't need another television. I left all the towel bars, tea cup / coffee cup hooks, the paper towel holder, spare tire, spare tire holder, even the drill bit extensions used for manually extracting the slides.
After the fact, I wish I would have tossed more stuff in the camper. I've found more items I removed, changed, altered in that camper and now have a pile of hardware and used parts I'll never use for anything, ever.
Did any of this add any extra value for the trade-in ... No. Absolutely none! But it was a good way for me to get rid of unwanted and unneeded RV stuff I knew I'd never, ever use again.
And by the way, our dealer did the same with us. We gave them all the information over the phone about the condition of the RV and they gave us an offer for the trade in. We had the option to accept it or decline it. I think the offer was low enough, that even if the trailer was completely wrecked, they'd still make money off of it at resale. That's how they do it you know. They don't have to see it. They are already offering a low enough price on trade in, they are not loosing anything.