I've been told, by RV salesperson no less, not to pay over NADA value.
She also said, in her opinion, rigs are overpriced now and the prices should be coming down.
Plus, it has to do with with what banks can loan to the buyer if you need to resell, and I think insurance also might not pay out more than NADA value in case of total loss. Basically, NADA is like home appraisal value. It is the accurate value because it's based on nationwide real sales data.
I'm a beginner in RV subject, so when I recently bought my first rig I had to pass on another very nice rig because it's been priced 10K over NADA, and I just didn't want to take the risk. Buying at NADA value or below gives some protection on resale in a downturn.
The rig I ended up buying was priced 5K under NADA value and in a very good condition with super low mileage.
But I only intend to keep the rig for 1-2 years. If you want to keep the rig forever, I'd at least inquire insurance companies if they'd ever pay out anything over NADA Value.