I agree that it is silly to actually quantify such values/preferences/whatnot--though it isn't impossible on an individual level--as the numbers would be fairly meaningless. But the framework is useful for understanding how we make our decisions.
If someone is willing to pay $500 dollars for a product with W,X,Y,Z as qualities (and those qualities capture everything about the product) and is only willing to pay $400 for another product with the qualities W,X,Y (and again assuming that those are all qualities, and that Z didn't in anyway enhance or detract from the other qualities), it's safe to assume that Z is worth $100 dollars to that person.
Framing is very important, and I think framing decisions like this, forcing the brain to approach decisions in such matter, will lead to decisions which will more accurately reflect our preferences (or what we would intellectually like our preferences to be, that behavior then possibly leading to an eventual change in preference. After buying a few SS suits, perhaps Rudals gets over his brand bias).
No longer in the realm of economics (at least, not in any but the loosest sense), but the subsequent question which could/should be addressed would be either "Given that I consider it worth the additional money, do I want it to be worth the additional money?" or "Given that I consider it worth the additional money, does this valuation accurately reflect my preferences?"
But you're the behavioral economist, so, uh,