Well, anyone can get slept on the first try. In fact, saves you make with additional attempts get easier, not harder.

That being said, int/wis does exert an effect on saves and that effect tends to feel more pronounced as your saves get really good. Made up numbers: let's say a gnome with max stats has 10% more chance to make his saves than a fire giant with max stats. Assume they always both carry the same amount of -save. When they have enough -save that the the fire giant makes his saves 50% of the time, the gnome's making his 60% of the time, which doesn't feel all that different. Suppose instead the fire's carrying enough to make his saves 80% of the time; now the gnome's clearing his 90% of the time and failing half as many saves. Now his mental stats feel like they mean a lot more, even if it's a static bonus.