I found myself visiting the RialtaHeaven site often as I was looking everywhere for a Rialta HD. Over several weeks and after reading nearly every description on virtually every advertising site in the U.S., I'd invariably wind up back at the "Heaven" site. And each time I'd cringe when I saw their prices.
My SO and I considered renting one of their units, the cost for which would apply to the purchase if we decided to buy, but that would have to have been planned for well before now, and while we weren't in a hurry, we also didn't want to wait 'til next Spring.
Brokers' prices were not too dissimilar to Heaven's, and while I have no problem with paying someone a finder's fee, I was not willing to pay the premium being asked. Just too high. And as you indicated in your query, NADA lists these in the mid-20's, which suggests Heaven's prices are definitely inflated. They will say the refurbishing costs justify the difference, which is partly true, but it doesn't address the NADA issue you raised. The fact is a vehicle can rarely get any better than "excellent" (near new appearance) so for me, at least, their prices simply don't justify an additional $10K....
Like 57lincolnman said, I'd rather put most of that difference into what I want in the Rialta.
(To 57lincolnman: looks like we share an interest in nearly-60-yr-old vehicles....I have a '57 T-bird in the garage.)