I agree. One thing that gets lost is that new folks to the hobby will get turned off if you're going deep into their pockets before they even walk through the door. And it is often overlooked that you will get money from them sooner or later, either via raffle ticket sales, SWAG purchases (T-shirts, pins, and the like), or indirectly via the vendor tables. That last one sounds odd, but the better the vendors do, the more likely they are to come back year after year, and the patrons will get that taste for the excitement that the Convention brings and they'll likewise keep coming back.
That's one reason our local show doesn't charge for walk-ins. Our vendor table rentals cover most of the venue costs, the contest supports itself, and the raffle fills the gap. As long as we break even on our local show, we're happy.
Cheers!
Ralph