I think people are fairly well convinced, and Strasburg won't sign unless that contribution is valued, so that is a good attitude if you're trying to provoke an impasse and assure that he goes to Japan or some such.
That's like saying you won't hire a salesman on a salary + commission basis, because you won't pay any guaranteed salary until he proves himself. The problem being, your competition will outbid you for the hire, and you will end up out of business due to lack of sales.
The Nats having only 5,000 in the stands is precisely why they so desperately need Strasburg. If he debuted in September (as Andrew Miller did the Sept. after being drafted out of UNC), I would bet the gate would be a season high.
One way people in real businesses weigh these things is to pay consultants to do market surveys. The surveys are not always accurate, of course, but you have to deal with the best information you have. If you simply say, "I won't pay until after you prove it," you will never have to pay because you'll never get the business opportunity in the first place.
If you've watched any O's games of late, all they can talk about is that tonight is Matusz's debut. They are a last place team trying to generate fan interest. On their weekend home stand, there were more BoSox fans in the stands than O's fans. With Detroit in town now, they need to sell tickets somehow.
Now, compare the number of people who know who Matusz is to the number who know who Strasburg is. Every Little Leaguer in a 100-mile radius will ask dad if he can go to that game. And come home with a tee shirt that says "Strasburg" across the back.