There is no sense in producing halo cars if you don't use elements in your mass production line. Styling bits, engineering (remember VTEC, anyone..?) or whatever. That's the trick. Let the Odyssey potential buyer see a hint of an NSX in there, and it can work in unifying your products.
But, those halo cars can make money. Porsche is very profitable. The cost of producing a Cayman, even in small-ish numbers is not 4-5x the cost of making a Corolla. Margins are large on $60K+ cars, and if you do it right, you don't have to make hundreds of thousands to earn a profit.