As someone who finances homes for a living, I will agree that the appraisals are apples to oranges when comparing to aircraft. Even at that there are still some similarities. Yes with homes you have comps available; however, appraisals don't always necessarily take into account market value. It is a formula based comparison to get a decent assessment of value from comps, but there are still intangibles that formulas and such can't quantify, and due to regulations, appraisers are limited in factoring in those variables for value. This is where in some instances appraised value isn't the same as market value. Aircraft are almost exclusively market value based. Case in point I paid a little more for my bird than most typical E models, but it was a rock solid plane that was flying very regularly and I was familiar with the plane itself and the previous owner. There is no way for that to be quantified on a report. When I used to fly for a living, I had started an aircraft brokerage department and quickly found Vref to not be that relevant. If you want to be in the ballpark of +/- 30%, I guess that can help.
In short, don't rely on Vref. That's my opinion from my experience.