Dan, my hypothesis is that the 432-card Indian Gum master set may always be unlikely to fetch its full "intrinsic value" (ie, value of all those individual, rare cards in the master set) because its unlikely there will ever be enough serious bidders, at any one time, to drive the price up, when this unusual item comes onto the market.
On the other hand, the standard 216-card R73 set is, I think, by its nature more attractive to the general market. Most vintage nonsport collectors should want one, either by building one or buying, and won't have to pay the premium associated with the rarer cards in the master set, like the Series of 288s and the white background portrait Series of 312 cards. The price is not cheap, but it's not so bad that it would drive folks away . . .
Some speculation: I wonder how much the Mastro winner could theoretically raise in selling off the 'extraneous' 200+ cards from the Mastro set, leaving a super-bargain net price for a very high grade 216-card basic set? (Lest Denis Kramer, father of that master set, feels a coronary coming on, please relax, buddy. Just playin' around, here!)
When you consider that almost one third of those cards that would be sold are really tough ones (48 x S288; 24 x S312 white background portrait cards), this subsidy might be very significant. Say, $125 each for the 24 lower S288s in unusually nice condition; $75 for the 24 higher ones; and perhaps say $100 each for the 24 white S312s in higher grade. There's something like $7k in recovered cost, give or take, and that's based on VERY conservative pricing (the low S288s if graded and in high condition can bring multiples of those price guesses) . . .
Just some random thoughts on a wintry morning!