The last time item trap boxes were fine with me was setting them at the apex of the loop in Mario Kart DS' Rainbow Road. Using psychological tactics, I set the box right in the middle of the road since people like to stay in the center of the road whenever possible. Usually, that's enough to hit them and set them back a really large distance. If I have the opportunity to again in a future lap, I set them more on the sides as now the other player will be expecting it in the center.
I've screwed over many a racer with tactics like that.
I would like to see something like Mario Kart 64's track handling. I'm glad Jelly mentioned it as I was thinking about how much I missed springing traps like Wario Stadium's jump or the massive Royal Speedway/Rainbow Road jumps. While they put other races who can't pull off the tricks at a huge disadvantage, the level of expertise needed to pull them off is so high that, as mentioned, one miscalculation in your velocity or trajectory and you're doomed to never see the top three unless you're racing a bunch of idiots.
Even then, the items in Mario Kart 64 had enough of a damage devastation that they could pretty much be the most balanced in the series. Even the Blue Shell is more than just a "Kill the bastard in First Place" weapon. Since it doesn't fly and instead travels along the ground, that homing beacon of death will nail EVERYONE who dares get in its way, making it so much more potent.