yes the level of play is higher in higher buyins. i don't play high buyins but from the small increases such as freerolls
vs $1 vs $2 vs $5 there's already a difference. this is just on average of course, you will always come across plays you completely disagree with. you will not notice the buy-in level by the cards they're playing, but see it in their level of thinking.
on a side note, i've seen some players do better in the higher buyins, probably because they bluff a lot more.