A little of both, but with a definite focus on quality.
First off- never buy any game I won't play, for any price. I don't like sports games, ultra-gory stuff, most racing games, & licensed things. No matter how cheap they are, I won't bother.
After that, there's a sort of price-to-personal value ratio that must be met for me to buy a game. For example: Babysitting Mama is not a good name, but it IS a very novel game with its plush baby controller accessory. I wouldn't pay full price. I wouldn't pay half price. But a dollar for a copy complete with plush baby? That I'll do. Most titles I have a vague interest in I'll buy at 5 bucks or less, more than that requires a greater interest in the title.
Like most people here, I've reached a point where most of the titles I'd want that are cheap I've already acquired. Given a choice between a couple titles of middling interest, or one expensive game of great interest, I'll usually get the expensive game. Funnily enough, space plays a role in this too- I'm a fair bit more picky about my PS4 games these days, becuase I have less space left on the PS4 shelf than the others. Same for NES/SNES. I've still got room for Switch, Xbox One, & Genesis though, so I'm a lot more likely to impulse buy those.