So, starting with the next big set, Magic is going to have about 25% less cards per set. And they're introducing "mythic rares", which you only get in about one out of every eight packs. I'm not entirely sure how I feel about that, but it could be interesting if they implement it right. They claim that they're going to use mythic rare slots for big, flashy rares like Legends, dragons, Planeswalkers, and that sort of thing, and not utility rares like Char, Thoughtsieze, or dual lands, which tend to be the most expensive rares already anyway. Statistically, mythic rares are twice as rare individually as regular rares (since there are only about a third as many mythic rares as rares, and that balances out the one in eight thing), and from now on, regular rares are going to be three-fourths as rare individually.
Theoretically this should mean that mythic rares are twice as valuable as they would be if they weren't mythic, and regular rares are 75% as valuable, so I stayed up too late last night teaching myself Excel to do some statistical analysis, calculating the overall price of rares for Lorwyn and Mirrodin, and seeing how the price would change if 23% of those cards were mythic and therefore cost twice as much, and if the others cost 75% as much, to a minimum of $1.00. It depends on what cards you consider mythic, but there's an overall price increase of anywhere from 4% to 20%. So mythic rares will likely make the game a little more expensive if you're going after singles, although it depends on what singles you're going for. And there's a couple other factors that I didn't consider: valuable uncommons will also be dropping 25% in price, and mythic rares have a higher chance of showing up in the foil slot than normal rares, so that might in fact offset things to more like a one in 7.5 chance of getting a mythic rare.
They sort of tried "ultra-rares" before with the Planar Chaos color-shifts, and it didn't really have a significant effect on their price. In my opinion, mythic rares are not particularly bad for the game, assuming that they stick to the guidelines they've said they will. But they're not particularly good for it either, and I don't understand their reasoning that adding ultra-rares attracts new players because its what players are used to in other card games.
Ultimately, though, the only way that mythic rarity makes a real difference is in buying singles. There's absolutely no effect on gameplay, and that's what I really care about. If anything, having fewer cards per set should hopefully lead to a higher overall card quality. It might be annoying if I'm trying to get four of some mythic rare that theoretically costs twice as much as it would have, but there's already ludicrously expensive cards even at regular rarity, and most of the ludicrously expensive cards I want, like dual lands, would hypothetically become cheaper. But I guess Connor is going to have some tough going buying giant indestructible colossi in the future.