Spells have mostly gotten slightly weaker. But creatures have only grown more and more powerful.
As for rares I don't think Richard Garfield ever intended to make it an expensive game. Magic is one of if not the first trading card game they didn't really know what they were getting into. They thought people might buy a handful of random cards (not 4x best card) and everyone might use different cards (whatever they had lying around). Closer to traditional kitchen magic. He never intended the game to be so expensive. And mythic rares weren't a thing for the first decade and a half.
Early on my playgroup literally just mixed all their cards together. We didn't really think of it as being "my deck" or whatever when we were playing unlimited. It wasn't really until Legends came out that anybody in my group of game friends started taking collectability or competitiveness seriously.
As for rares I don't think Richard Garfield ever intended to make it an expensive game. Magic is one of if not the first trading card game they didn't really know what they were getting into. They thought people might buy a handful of random cards (not 4x best card) and everyone might use different cards (whatever they had lying around). Closer to traditional kitchen magic. He never intended the game to be so expensive. And mythic rares weren't a thing for the first decade and a half.